Research: Cry It Out (CIO) Sleep Training

Generated: 2026-02-27 Status: Complete

TL;DR

CIO (extinction) and Ferber (graduated extinction) both work for most babies 4-6+ months old, typically within 3-5 nights. The best available evidence (multiple RCTs, one 5-year follow-up) shows no long-term harm to attachment, behavior, cortisol, or parent-child relationship. However, all studies are small-to-moderate in size, culturally narrow (mostly Australian/Western), and no data exists beyond age 6. The NHS and attachment-oriented communities oppose CIO; the AASM and Australian guidelines support it. Baby temperament is the biggest predictor of whether it works. About 10-20% of babies do not respond well. It is reasonable to try CIO if sleep deprivation is unsustainable, and equally reasonable not to — the evidence genuinely supports either choice.

Research Findings

Source: PubMed

Age and Timing

Earliest safe age: 4-6 months; most evidence supports 6 months+

Most clinical trials enroll infants aged 6-16 months. No studies were identified that used unmodified or graduated extinction in infants under 4 months of age. The strongest evidence base is for infants 6 months and older, when circadian rhythms and sleep architecture are sufficiently developed to support consolidated nighttime sleep.

• Gradisar et al. (2016) enrolled infants aged 6-16 months in their RCT (PMID: 27221288).
• Pennestri et al. (2018) — Longitudinal cohort, n=388. Found that 28-57% of infants at 6 and 12 months do not sleep through the night (defined as 6-8 hour uninterrupted blocks), and that this is developmentally normal. No associations were found between sleeping through the night and concurrent or later mental/psychomotor development (Bayley Scales) or maternal mood (CES-D) at 6, 12, or 36 months. However, sleeping through the night was associated with significantly lower breastfeeding rates (P < .0001). This suggests that expectations for early sleep consolidation may be unrealistic and that CIO before 6 months may address a non-problem. Evidence grade: B (large cohort, validated measures, but observational). PMID: 30420470.

Short-Term Effects

Cortisol and Stress

• Gradisar et al. (2016) — RCT, n=43 infants (6-16 months), randomized to graduated extinction (n=14), bedtime fading (n=15), or sleep education control (n=14). Salivary cortisol was sampled mornings and afternoons. Both intervention groups showed small-to-moderate declines in cortisol relative to controls — not increases. Maternal stress also decreased in both intervention groups over the first month. Evidence grade: B (RCT with objective biomarker, but small sample limits power). PMID: 27221288.

• Middlemiss et al. (2012) — Observational study, n=25 infants (4-10 months), 5-day inpatient extinction program. By day 3, infants no longer cried at sleep onset, but their salivary cortisol levels remained elevated at the post-sleep-onset sampling. Mothers’ cortisol decreased (no longer hearing crying), creating a mother-infant cortisol asynchrony. This study is frequently cited as evidence of “hidden” physiological stress despite behavioral compliance. However, it has significant methodological limitations: very small sample (n=25), inpatient hospital setting (not representative of home environment), no control group, cortisol measured at only two time points per day, and no long-term follow-up. Evidence grade: C (small, uncontrolled, non-naturalistic setting, no comparison group). PMID: 21945361.

Sleep Outcomes

• Gradisar et al. (2016) — Graduated extinction produced large decreases in number of awakenings (P < .0001) and wake after sleep onset (P = .01). Both graduated extinction and bedtime fading produced large decreases in sleep latency (P < .05). Outcomes were confirmed by both parent-reported sleep diaries and objective actigraphy. Evidence grade: B (RCT with objective measurement, small n). PMID: 27221288.

• Mindell et al. (2006) — Systematic review of 52 treatment studies commissioned by the American Academy of Sleep Medicine. Found that 94% of studies reported behavioral interventions were efficacious, with over 80% of treated children showing clinically significant improvement maintained for 3-6 months. Both unmodified extinction and graduated extinction were classified as having strong empirical support (Level 1 evidence). The review covered a range of ages from birth to 5 years. Evidence grade: A (comprehensive systematic review across multiple RCTs and controlled studies). PMID: 17068979.

• Hiscock & Wake (2002) — RCT, n=156 mothers of 6-12 month old infants with parent-reported sleep problems, randomized to controlled crying intervention vs. well-child care control. At 2 months post-intervention, intervention group infants had significantly fewer sleep problems and mothers had significantly lower depression scores on the Edinburgh Postnatal Depression Scale. Evidence grade: B (moderate-sized RCT, short follow-up).

Maternal Mental Health (Short-Term)

• Hiscock et al. (2007) — Cluster RCT, n=328 mothers from 49 Maternal and Child Health centres in Melbourne, Australia. Infants were 7 months at enrollment. Behavioral sleep intervention (controlled comforting / camping out) significantly reduced maternal depression symptoms at the 10-month follow-up compared to controls. Evidence grade: A (large population-based cluster RCT). PMID: 17158146.

Long-Term Effects

Attachment Security

• Gradisar et al. (2016) — At 12-month follow-up, mother-child dyads underwent the Strange Situation Procedure (the gold-standard experimental assessment of attachment security). No significant differences in secure vs. insecure attachment classifications were found between graduated extinction, bedtime fading, and control groups. This is the only RCT to use the Strange Situation Procedure to assess attachment after sleep training. Evidence grade: B (RCT with validated gold-standard measure, but small n=43 limits statistical power to detect small effects). PMID: 27221288.

Child Behavior, Emotional Health, and Stress Regulation

• Price et al. (2012) — 5-year follow-up of 326 children (173 intervention, 153 control) from the Hiscock et al. (2007) cluster RCT. At age 6, children were assessed on emotional/behavioral problems (Strengths and Difficulties Questionnaire), sleep habits, diurnal salivary cortisol, BMI, and parent-child relationship quality. No significant differences were found on any measure between children whose parents received behavioral sleep intervention in infancy and controls. This is the longest follow-up of any sleep training RCT and provides the strongest evidence that behavioral sleep interventions do not cause long-term harm. Evidence grade: A (large RCT with 5-year follow-up, validated multi-domain assessment, adequate retention). PMID: 22966034.

• Hiscock et al. (2008) — 2-year follow-up of the same cluster RCT (n=328). At age 2, intervention mothers were less likely to report clinical depression (15.4% vs. 26.4%). No adverse effects were detected on children’s mental health, behavioral problems, or mothers’ parenting practices. Evidence grade: A (large cluster RCT, population-based, 2-year follow-up). PMID: 18762495.

• Gradisar et al. (2016) — At 12 months post-intervention, no significant group differences on the Child Behavior Checklist. Evidence grade: B. PMID: 27221288.

Extinction vs. Graduated Extinction (Ferber)

Definitions:

• Unmodified extinction (“cry it out” / CIO): Parent puts infant to bed drowsy but awake and does not return until a preset morning wake time. Typically produces faster results (3-5 nights) but higher initial parental distress and lower acceptability.
• Graduated extinction (Ferber method / controlled crying): Parent checks on infant at progressively longer intervals (e.g., 3, 5, 10, 15 minutes) without picking up. Takes slightly longer to achieve results (5-7 nights) but is more tolerable for most parents.
• Bedtime fading: Parent temporarily delays bedtime to align with the infant’s natural sleep onset, then gradually moves bedtime earlier. No crying is involved. Slower to produce results but highest parental acceptability.

Head-to-head comparison:

• Gradisar et al. (2016) directly compared graduated extinction to bedtime fading. Graduated extinction showed superior outcomes on number of awakenings and wake after sleep onset compared to bedtime fading, though both methods outperformed controls on sleep latency. PMID: 27221288.
• Mindell et al. (2006) classified both unmodified extinction and graduated extinction as having equivalent levels of empirical support for efficacy. The AASM rated unmodified extinction slightly higher (Standard vs. Guideline), but this reflected the volume and consistency of evidence rather than demonstrated superiority. The choice between methods is primarily a matter of parental preference and tolerance, not differential efficacy or safety. PMID: 17068979.

Evidence Summary Table

Limitations and Gaps in the Literature

1. Small sample sizes: The only RCT comparing specific methods (Gradisar 2016) had just 43 participants. Larger replication studies are needed.
2. Self-selection bias: Families who enroll in sleep training studies may differ systematically from those who do not (e.g., higher distress tolerance, more motivation).
3. Measurement timing: Cortisol studies typically sample at limited time points; continuous cortisol monitoring would provide more complete data.
4. Cultural homogeneity: Nearly all RCTs were conducted in Australia or the US/UK with predominantly white, middle-class families. Generalizability to other cultural contexts is uncertain.
5. No studies beyond 6 years: The longest follow-up is Price et al. (2012) at 5 years. Effects on adolescent or adult outcomes remain unknown.
6. Lack of head-to-head RCTs: No large RCT has directly compared unmodified extinction to graduated extinction to a no-intervention control.

Official Guidelines

Source: AAP, AASM, WHO, NHS, Australian MCRI

American Academy of Sleep Medicine (AASM) — 2006 Practice Parameters

The most authoritative clinical guideline on behavioral sleep interventions for infants and young children comes from the AASM (Morgenthaler et al., 2006, SLEEP 29(10):1277-1281). The task force reviewed 52 treatment studies and found that 94% yielded clinically significant improvement, with 82% of treated infants and young children benefiting. The recommendations use a three-tier evidence grading system (Standard > Guideline > Option):

Standard (highest evidence level):

• Unmodified extinction (full CIO) — rated as individually effective for bedtime problems and night wakings
• Extinction with parental presence — rated as individually effective
• Preventive parent education — rated as individually effective

Guideline (moderate evidence level):

• Graduated extinction (Ferber method / controlled crying) — rated as individually effective but with less certainty
• Bedtime fading / positive routines — rated as individually effective but with less certainty
• Scheduled awakenings — rated as individually effective but with less certainty

Option (insufficient evidence):

• Standardized bedtime routines and positive reinforcement alone — insufficient evidence to recommend as single therapies

The AASM recommends behavioral interventions before pharmacological approaches: medications should not be prescribed for childhood insomnia unless behavioral interventions are unsuccessful or not indicated.

Age range studied: 0-4 years 11 months (i.e., birth through age 5).

Supporting review: Mindell et al. (2006), “Behavioral treatment of bedtime problems and night wakings in infants and young children” (SLEEP 29(10):1263-1276), which served as the evidence review underpinning these practice parameters.

American Academy of Pediatrics (AAP)

The AAP does not publish a standalone clinical practice guideline specifically on sleep training methods. However, the AAP’s position can be synthesized from multiple sources:

• HealthyChildren.org (AAP’s parent-facing site) acknowledges sleep training as an appropriate strategy and describes graduated extinction as a valid method. The AAP advises that babies can begin to learn self-soothing skills as part of healthy sleep habits.
• Gradisar et al. (2016), published in Pediatrics (the AAP’s flagship journal), is the key RCT. This study of 43 infants aged 6-16 months found that graduated extinction and bedtime fading both significantly improved sleep latency and night wakings, with no adverse effects on infant cortisol, attachment security, or emotional/behavioral outcomes at 12-month follow-up.
• Price et al. (2012), also in Pediatrics 130(4):643-651, conducted a five-year follow-up of behavioral infant sleep intervention and found no long-term harms to children’s emotional health, behavior, sleep quality, stress regulation, or the child-parent relationship.
• Age recommendation: Most AAP-affiliated pediatricians recommend starting sleep training no earlier than 4-6 months of age (specifically around 16 weeks and 14 pounds), when a baby’s circadian rhythm is more established and they are developmentally capable of self-soothing. The AAP has not set a formal upper age limit.

Evidence grade: No formal AAP evidence grade assigned. The supporting RCTs are Level I-II evidence.

World Health Organization (WHO)

The WHO has not issued a specific position on sleep training methods such as CIO or graduated extinction. WHO guidelines on infant sleep focus on:

• Sleep duration: 14-17 hours for infants 0-3 months; 12-16 hours for infants 4-11 months (WHO Guidelines on Physical Activity, Sedentary Behaviour and Sleep for Children Under 5 Years of Age, 2019)
• Safe sleep environment: Supine sleeping position during the first year, quiet environment, safe bedding
• Responsive caregiving: WHO’s Nurturing Care Framework (2018) emphasizes responsive caregiving as foundational, but does not specifically address or prohibit behavioral sleep training

The absence of a WHO position on sleep training is notable. This is likely because sleep training is primarily a concern in Western/individualistic cultures where separate infant sleep is normative.

UK National Health Service (NHS)

The NHS takes a more cautious stance than US organizations:

• NHS services generally do not recommend sleep modification techniques that involve leaving a baby to cry, such as unmodified extinction (full CIO) or controlled crying
• NHS guidance advises against leaving a baby to cry for longer than 7-8 minutes
• The emphasis is on responsive parenting and establishing consistent routines rather than extinction-based techniques
• No formal NICE (National Institute for Health and Care Excellence) clinical guideline exists specifically on infant sleep training

Evidence grade: No formal evidence grade. The NHS position reflects a precautionary/responsive-parenting philosophy rather than a systematic evidence review of sleep training per se.

Australia — Murdoch Children’s Research Institute (MCRI) / RACGP

Australia has some of the most supportive and well-researched guidelines on sleep training:

• Controlled comforting (graduated extinction) and camping out (extinction with parental presence) are recommended as evidence-based strategies for infants 6 months and older
• Research led by Professor Harriet Hiscock at MCRI demonstrated that these techniques are effective in approximately 80% of babies and safe for well infants
• A five-year follow-up study found no long-term harm to children’s development, health, or wellbeing
• The Royal Australian College of General Practitioners (RACGP) endorses controlled comforting as an evidence-based intervention
• Sleep training is integrated into routine maternal-child health services in many Australian states

Evidence grade: Based on RCT evidence (Hiscock et al., 2007, BMJ; Hiscock et al., 2008, Pediatrics).

Australian Association for Infant Mental Health (AAIMH)

The AAIMH published a position paper expressing concerns about controlled crying, particularly regarding potential stress on the infant and the importance of responsive caregiving. This represents a minority professional dissent from the broader Australian clinical consensus.

Canadian Paediatric Society (CPS)

The CPS has not published a specific position statement on sleep training methods. Their guidance focuses on safe sleep environments and SIDS prevention. The Canadian Sleep Society’s pediatric sleep position statement addresses sleep development but does not make specific recommendations for or against extinction-based methods.

Key Differences Between Organizations

Age Recommendations Summary

• No organization recommends sleep training before 4 months of age
• 4-6 months is the most commonly cited minimum age (AAP-affiliated guidance, Sleep Foundation, most pediatric sources)
• 6 months is the minimum in Australian protocols (MCRI/RACGP)
• The AASM’s 2006 evidence review included studies of infants from birth, but in practice, most clinicians recommend waiting until at least 4 months when circadian rhythms mature

Contraindications (consensus across guidelines)

No organization recommends sleep training when:

• The infant has an acute illness or undiagnosed medical condition (e.g., reflux, ear infection)
• The infant is not gaining weight appropriately or has failure to thrive
• There are concerns about neglect or unsafe home environment
• The parent has untreated severe mental health issues that impair judgment
• The infant is premature (adjusted age should be used for developmental readiness)

Community Experiences

Source: Reddit (r/sleeptrain, r/beyondthebump, r/ScienceBasedParenting, r/AttachmentParenting, r/NewParents)

Success Stories

The majority of parents who post about CIO on r/sleeptrain report positive outcomes, often with dramatic before/after contrasts. A recurring pattern is parents who were initially against CIO but eventually tried it out of desperation.

“I was adamantly against CIO. Any time someone would mention they were using this method to sleep train their kid, I was silently judging them. I thought it was cruel, barbaric, and harmful… But then my LO needed to transition from bed-sharing to his own crib… and CIO was the only method that worked.” — u/[OP], r/sleeptrain (source)

“I was adamantly against sleep training. I held out for 13 months suffering every single night. My daughter would literally wake up every hour expecting to comfort nurse… CIO is literally the best thing I’ve ever done for both of us.” — u/[OP], r/sleeptrain (source)

“Ok hear me out - my life and mental health completely changed for the better once we decided to sleep train our then 8.5 month old… by night 5 SHE WAS GOING TO SLEEP ON HER OWN with a smile on her face and literally ZERO tears.” — u/[OP], r/sleeptrain (source)

“I keep seeing people say how sleep trained babies are so sad and stressed, and they just give up on seeking their parents’ help. But that can’t be further from the truth!!! I watch my son sleep on his monitor every night and either I’m a really dense psychopath who can’t read emotions, or he’s just content to go to sleep himself.” — u/catskii, r/sleeptrain (source)

“I got incredibly wrapped up in the varying opinions of baby sleep influencers and was deeply afraid of allowing my baby to cry ever. I spent HOURS in my baby’s room trying to transfer him to his crib fully asleep, just for him to wake up every 45m until I would give up and cosleep the remainder of the night. For 10 months.” — u/[OP], r/sleeptrain (source)

“The made a fool of myself on this sub is so real. I ended up doing CIO and I was like oh ffs I could have been doing this for literally 3+ months what was I doingggg” — u/Correct-Produce84, r/sleeptrain (source)

How Long It Took

Most parents who report success describe significant improvement within 3-5 nights. The pattern is often: hardest night is night 1, dramatic improvement by night 2-3, and near-zero crying by night 5-7.

“Night 1 she cried for [a long time]… night 2 she cried for 4 minutes and then fell asleep. Night 4 was 10 minutes and no night wakes. Day 5 was NO CRYING at all to fall asleep.” — u/[OP], r/sleeptrain (source)

“First night was so hard but she only cried for 20 minutes before falling asleep. By the third night she only fussed for 5 minutes.” — u/[OP], r/sleeptrain (source)

“We sleep trained our son at 5 months using full extinction. He cried less than 15 min that first night, and did less every night after that.” — u/[OP], r/sleeptrain (source)

“My husband told me to go sleep at my moms while he sleep trained. Zero regrets. He did it at 6 months and it took 3 nights. She is 13 months now and has slept 10-12 hours straight since.” — u/beatleslisa, r/beyondthebump (source)

However, some parents report it taking longer or not fully resolving:

“On night 6 and still having long periods of crying ~25 minutes. Did have one night of no crying on night 4.” — u/[OP], r/sleeptrain (source)

“We tried a gentle Ferber and had to quit after a MONTH because she still screamed for at least 20 minutes every night, wouldn’t be calmed by anything except being picked up.” — u/bothersomeblueberry, r/sleeptrain (source)

Age They Started

The most common ages reported by parents are 4-6 months (the earliest most pediatricians recommend) and 8-10 months (often after the 4-month regression has stretched into months of poor sleep). A smaller group starts at 12+ months after exhausting other methods.

• 4 months: “Sleep training was the best thing I ever did. We did it at 4 months and my 5.5 month old sleeps 12 hours most nights.” — u/daniohh, r/sleeptrain (source)
• 5 months: Most commonly cited as the “sweet spot” in r/sleeptrain. Multiple parents report success at this age with minimal total crying.
• 6 months: “We went from waking up hourly and 30 minute naps to 7+ hour chunks and 1.5 hour naps within 2 weeks. It was WAY easier and less scary than I anticipated.” — u/[OP], r/sleeptrain (source)
• 8.5 months: A common “crisis point” age where parents who were initially against CIO finally try it after months of worsening sleep.
• 10-13 months: “I was adamantly against sleep training. I held out for 13 months suffering every single night.” — u/[OP], r/sleeptrain (source)
• 3 months (controversial): One thread on r/NewParents asks “Is three months too young to use the cry it out method?” The consensus is yes — most experts and parents agree 4 months is the absolute minimum, with many preferring to wait until 5-6 months. (source)

Struggles and Emotional Toll

Even parents who report success describe CIO as emotionally excruciating. Several themes emerge: parental guilt, judgment from family, and the physical difficulty of listening to crying.

“I found it excruciating, and had to leave the house and stay away until my husband texted me the all clear (my husband also hated to hear him cry, but he took one for the team on this).” — u/[OP], r/sleeptrain (source)

“I feel extreme guilt and embarrassment when we have people over and he cries. When we had family visiting, I just stayed in his room while he CIO for a bit so they didn’t judge me for leaving a crying baby (my family is very against CIO and don’t know that we sleep trained).” — u/Either_Bread_8253, r/sleeptrain (source)

“My first child is 3 and I still feel so much guilt over sleep training him that it makes me nauseous if I think about it… We essentially did extinction with him around 6-8 months after trying gentler methods and being delirious from exhaustion. It worked, but within a couple of months I regretted it.” — u/[OP], r/beyondthebump (source)

“I had this weird gut instinct dreadful feeling that this was just wrong every time she cried to sleep… missed bonding with her and rocking her, it made me so sad when she wouldn’t be able to sleep with me in the room.” — u/rushi333, r/beyondthebump (source)

A notable drawback frequently mentioned is that sleep-trained babies can become inflexible sleepers — they only fall asleep in their crib with their exact routine:

“I cannot get her to sleep in any other environment other than the car, so it is a very inflexible situation… My family wants to go on a big vacation in the spring and we very likely will be staying behind because I don’t want to risk her not being able to sleep.” — u/alsothebagel, r/sleeptrain (source)

“She has a hard time sleeping in the plane, sleeping on the floor when we go see family, sleeping with us in bed when we go on vacation, etc. It stresses me to take her somewhere that does not have a crib.” — u/moroccan___, r/sleeptrain (source)

Regrets and Guilt

A significant thread on r/beyondthebump explored lingering guilt years after CIO. The OP described ongoing nausea when thinking about it, despite their child being happy and well-adjusted. Community responses were overwhelmingly reassuring:

“Taking care of your baby while deliriously sleep deprived is more harmful to your baby than CIO is, and I will die on this hill.” — u/cucumberswithanxiety, r/beyondthebump (source)

“Independence is the BIGGEST sign of secure attachment, just FYI. Don’t have that part be a reason for guilt!” — u/Apprehensive_Buy4920, r/beyondthebump (source)

“Sleep deprivation is considered torture under the Geneva convention. As in, it’s technically illegal to deprive someone of sleep repeatedly over extended periods of time, because it can genuinely make you insane. Like ‘shake your baby in a fit of rage’ bad. So do not feel guilty for sleep training your kid.” — u/Coxal_anomaly, r/beyondthebump (source)

When CIO Did Not Work or Caused Harm

Not all experiences are positive. Some parents report that CIO backfired or was clearly wrong for their child:

“One of my wife’s friends enthusiastically convinced us to sleep train our LO with the same method that worked wonders for her… By day 4, our LO started [showing behavioral changes].” — u/[OP], r/beyondthebump (source)

“Every kid has a different temperament. My son would have been the same as yours, there’s no way we could have done it even if we wanted to. He will vomit on himself from stress if we can’t get to him quick enough, it’s awful.” — u/m00nje11y, r/beyondthebump (source)

“A doctor told me to do very light sleep training when my son was around 13/14 months. I tried it exactly once when he had just turned 15 months. He got so upset when I wouldn’t pick him up after less than 5 minutes that I couldn’t console him after picking him up. I’m never doing that again.” — u/ApplesandDnanas, r/AttachmentParenting (source)

“We tried sleep training for a year, although probably never truly stuck to it because my husband hated to hear the crying and would freak out every time… I don’t know what my next baby will be like, but this kid never made it easy on me!” — u/FunProgram3702, r/sleeptrain (source)

Anti-CIO Perspectives

The r/AttachmentParenting community is overwhelmingly against CIO. When a parent posted that their pediatrician recommended CIO at 6 months, the top response (261 upvotes) was:

“I really think there would be far fewer problems in the world if more babies were held for longer by their mothers.” — u/gnox0212, r/AttachmentParenting (source)

“The only time you need to start sleep training is if what you’re doing doesn’t work for you.” — u/Infinite853, r/AttachmentParenting (source)

“CIO is not self soothing. It’s just giving up that help is ever going to come. Generally, I have not seen a child able to self sooth until 1.5… You can sleep train a child pretty early, but you can’t teach them to self sooth for a long while and they need to borrow your calm for quite some time, like years.” — u/Intelligent_You3794, r/AttachmentParenting (source)

Cultural perspectives also challenge CIO as a primarily American phenomenon:

“My theory on it is that CIO is and was popular in the USA because it allows mums and dads who don’t get any maternity or paternity leave to sleep more… I have friends who went back to work or were single, and CIO is the only way they could survive. I had 16 months maternity leave, my baby just started to sleep through the night when I weaned him from BF overnight. I had the luxury and privilege to never need CIO.” — u/Unepetiteveggie, r/ScienceBasedParenting (source)

A therapist posting on r/ScienceBasedParenting offered a cautious view:

“While I completely understand why many parents feel the need to sleep train their babies, there are more drawbacks to sleep training than a simple google search would have you believe… Babies are wired through years and years of evolution to need your comfort and support to help them sleep and coregulate.” — u/[OP], r/ScienceBasedParenting (source)

What the Science Actually Says (Per Reddit Discussion)

A highly upvoted comment on r/ScienceBasedParenting summarized the state of the evidence:

“We don’t have good evidence one way or the other. What we have are credible theories — one that sleep training can promote better outcomes in children due to improvement in caregiving outside of sleep hours when everyone rests better, and two, that sleep training can cause worse outcomes in children due to the experience of limited responsiveness creating stress or harming attachment. Anyone who is trying to convince you of one of the above will cite some studies, but none are very good. This is really an area where, as a parent trying to follow the science, you can choose what works best for your family and kids without guilt.” — u/Apprehensive-Air-734, r/ScienceBasedParenting (source)

The same commenter noted that the longest follow-up study (5 years) found: “Sleep training improves infant sleep problems, with about 1 in 4 to 1 in 10 benefiting compared with no sleep training, with no adverse effects reported after 5 years.”

Long-Term Observations

Parents who posted 17+ months after sleep training reported:

• Sleep quality remained strong but periodic retraining was needed after illness, travel, or teething
• No observable attachment issues — children were described as happy, affectionate, and secure
• Inflexibility was the most common drawback — sleep-trained babies often could not sleep outside their usual environment
• Subsequent children sometimes responded differently — what worked for one child did not always work for the next

“Extremely relatable post! Our daughter turns 2 very soon and we also sleep trained at 5 mos. Everything you went through mirrors our experience including the retraining for sickness, guests, etc. We accepted the fact that sleep training and re-training is going to be a thing for a while. But overall - it was the best decision made and never looked back!” — u/VHRose01, r/sleeptrain (source)

“I sleep trained my first baby, and he was always a good sleeper after that… Number 2 was naturally a better sleeper, although we did some sleep training… Number 3 is currently 9 months and I’ve been least consistent with her sleep, and sleep has been a bigger struggle because of that.” — u/BubblyCountryMama, r/sleeptrain (source)

Common Patterns Across Communities

1. Desperation is the primary driver: Nearly every CIO success story begins with months of severe sleep deprivation, failed gentler methods, and deteriorating parental mental health.
2. Ferber vs. full extinction: Many parents start with Ferber (timed check-ins) and switch to full extinction after finding check-ins made crying worse. Others find Ferber sufficient.
3. Partner alignment matters: Several failed attempts were attributed to one parent being unable to commit, undermining consistency.
4. Social media and influencer culture is frequently blamed for causing unnecessary guilt and fear around CIO.
5. The debate is deeply polarized: r/sleeptrain is overwhelmingly pro-CIO, r/AttachmentParenting is overwhelmingly anti-CIO, and r/ScienceBasedParenting acknowledges the evidence is inconclusive either way.
6. Temperament is key: Multiple parents note that CIO worked perfectly for one child but was clearly wrong for another, suggesting individual baby temperament is a major factor in outcomes.

Cultural & International Perspectives

Key insight: CIO is largely a phenomenon of countries with limited parental leave. Parents in countries with 12+ months of leave rarely feel the need for extinction-based sleep training because they can afford to wait for developmental readiness. This does not make CIO harmful — it means the need for it is partly structural, not purely developmental.

Viewpoint Matrix

Decision Framework

Consider CIO/Ferber if:

• Baby is 4-6+ months (ideally 5-6 months; circadian rhythm established)
• Current sleep situation is unsustainable (parental mental health, safety concerns from exhaustion)
• Gentler methods (bedtime fading, pick-up/put-down) have been tried and failed
• Both parents/caregivers are aligned and committed to consistency
• Baby is healthy, gaining weight well, no acute illness
• You have 3-5 nights where you can commit fully without travel or visitors

Alternatives to try first:

• Bedtime fading — no crying, delay bedtime to match natural sleep onset, gradually move earlier
• Pick-up/put-down — respond to crying, put down when calm, repeat
• Chair method / camping out — gradual parental withdrawal from room over 1-2 weeks
• Optimize sleep hygiene — dark room, white noise, consistent routine, appropriate wake windows
• Wait — many babies naturally consolidate sleep by 9-12 months without intervention

Red flags — stop CIO immediately if:

• Baby is vomiting from distress (not spit-up, actual stress vomiting)
• Crying is escalating after 5+ nights rather than decreasing
• Baby shows daytime behavioral changes (increased clinginess, withdrawal, regression)
• Parent’s gut feeling says something is genuinely wrong (not just discomfort — trust acute distress signals)
• Baby has an undiagnosed medical issue (reflux, ear infection, teething pain)

Age-Specific Guidance Table

Summary

Cry It Out (CIO) and graduated extinction (Ferber) are the most studied behavioral sleep interventions for infants. The evidence base — anchored by the AASM’s 2006 systematic review of 52 studies, the Gradisar 2016 RCT, and the Price 2012 five-year follow-up — consistently shows that these methods are effective for most babies (80-94% improvement rates) and do not cause measurable harm to attachment, cortisol regulation, behavior, or parent-child relationships up to age 6.

However, the evidence has real limitations. Sample sizes are small (the key RCT had only 43 infants). All major studies come from Australia, the US, or the UK with predominantly white, middle-class participants. No data exists beyond 6 years of age. The one study frequently cited as showing harm (Middlemiss 2012, cortisol asynchrony) has serious methodological problems and no control group.

The international picture reveals that CIO is largely a Western phenomenon driven by structural factors — particularly limited parental leave. Countries with generous leave (Nordic, Japan) rarely practice or study sleep training because the economic pressure to consolidate infant sleep early simply doesn’t exist.

Parent experiences are deeply polarized. The majority of parents who try CIO report dramatic success within 3-5 nights and describe it as life-changing. A meaningful minority report that it backfired — their baby escalated, vomited, or showed behavioral changes. Baby temperament appears to be the most important variable in predicting success. The emotional toll on parents is significant regardless of outcome, with guilt persisting for years in some cases even when the child thrives.

The honest synthesis is: CIO is probably safe and effective for most babies over 5-6 months, but the evidence isn’t strong enough to be certain, and it clearly doesn’t work for every baby. The choice should be driven by family circumstances, baby temperament, and parental values — not guilt in either direction.

Key Takeaways

1. Start no earlier than 4 months, ideally 5-6 months — no organization recommends sleep training before 4 months; the strongest evidence is for 6+ months when circadian rhythms are mature.
2. Most babies respond within 3-5 nights — night 1 is hardest, with dramatic improvement by night 2-3; if crying is still escalating after 5-7 nights, reassess.
3. No measurable long-term harm at 5 years — the Price 2012 study (n=326) found no differences in behavior, cortisol, sleep, or parent-child relationship at age 6. This is the strongest evidence available.
4. The cortisol “harm” study is weak — Middlemiss 2012 (n=25, no control, hospital setting) is the most-cited anti-CIO study but has major methodological limitations.
5. Baby temperament is the biggest variable — CIO works brilliantly for some babies and clearly fails for others; there is no way to predict in advance which camp your baby falls into.
6. Ferber and full CIO have equivalent efficacy — choose based on parental tolerance; many parents find Ferber check-ins actually increase crying and switch to full extinction.
7. Sleep-trained babies may become inflexible sleepers — a common trade-off is that they struggle to sleep outside their crib/routine (travel, family visits).
8. Periodic retraining is normal — illness, travel, and developmental leaps often require 1-2 nights of re-training; this is expected, not failure.
9. CIO is largely a Western/American phenomenon — countries with generous parental leave rarely need or practice it; the “need” is partly structural, not purely developmental.
10. Both choices are defensible — the evidence genuinely supports either trying CIO or choosing not to; make the decision based on your family’s circumstances without guilt.

Related Topics

• Infant Sleep 0-3 Months
• Newborn Co-sleeping & Habit Formation
• Soothing Crying Newborns
• Parental Leave, Rest & Self-Care