Sleep Training Research: What We Know, What We Don’t, and Why Context Matters

By Birth & Baby University · Last updated: October 2026 · 8 min read

Sleep training is one of the most polarizing subjects in parenting, and one on which evidence has been interpreted in opposite directions by people reading the same studies. Postpartum doulas work mainly in the first months, before most sleep training begins, but they are regularly asked about it, sometimes by parents who are exhausted and sometimes by parents worried that it will harm their baby. The honest picture is that randomized trials exist, mostly in babies older than six months, that they show short- to medium-term sleep benefits without detected long-term harm, and that their results do not transfer cleanly to newborns. This article summarizes what the studies show, where critics and supporters disagree, and why context matters for a postpartum doula.

Key takeaways

Quick answer: for infants roughly 6 months and older, trials of behavioral sleep methods such as graduated extinction and bedtime fading show improved sleep and no detected long-term harms to attachment, behavior or mental health in the follow-ups studied. For babies younger than 6 months, a systematic review concluded that behavioral sleep interventions have not been shown to improve outcomes. The newborn period is not a time for sleep training, and a doula should not recommend or conduct it.

• A randomized trial of 43 infants aged 6 to 16 months found graduated extinction and bedtime fading both improved sleep above a control, and at 12 months showed no differences in emotional and behavioral problems or attachment.
• A five-year follow-up of a trial that gave a behavioral program to parents of 7-month-olds with sleep problems found no differences at age 6 in children’s emotional or conduct scores, sleep problems, stress, parent-child relationship or maternal mental health.
• A cohort of 178 infants found that parents leaving infants to cry it out in the first 6 months was not associated with adverse effects on attachment and behavior at 18 months.
• A systematic review of behavioral sleep interventions in infants younger than 6 months concluded they have not been shown to decrease infant crying, prevent later sleep or behavioral problems or protect against postnatal depression, and may carry risks such as premature cessation of breastfeeding and increased maternal anxiety.

What the research says

Trials in older babies. Gradisar and colleagues’ 2016 randomized trial in Pediatrics assigned 43 infants aged 6 to 16 months to graduated extinction (14), bedtime fading (15) or sleep education control (14). Both methods reduced sleep latency; graduated extinction also reduced awakenings and wake after sleep onset. Salivary cortisol showed small-to-moderate declines with the interventions compared with controls, mothers’ stress decreased over the first month, and at 12 months there were no differences in children’s emotional and behavioral problems or in attachment style. The authors concluded the methods convey no adverse stress responses or long-term effects on attachment or child emotions. The study is small, parent-reported sleep diaries supplemented actigraphy, and it studied babies who already had sleep problems and were older than six months. Price and colleagues’ five-year follow-up (2012) of a cluster-randomized trial followed 225 of 326 families whose 7-month-olds had parent-reported sleep problems and received behavioral techniques in one to three nurse consultations. At age 6 they found no evidence of difference between intervention and control for child emotional and conduct scores, sleep problems (9% versus 7%), child-parent closeness and conflict, disinhibited attachment, chronic stress or parent depression, anxiety and stress. The authors concluded that behavioral sleep techniques have no marked long-lasting effects, positive or negative. About a third of families were lost to follow-up, and these were children with parent-reported sleep problems.

Cry-it-out and younger infants. Bilgin and Wolke’s 2020 longitudinal study followed 178 infants and their caregivers in the UK from birth to 18 months. Leaving infants to cry it out was rare at term and increased with age. Use at term was associated with less crying at 3 months, and use a few times at term and often at 3 months was associated with shorter fuss and cry duration at 18 months. No adverse impacts on attachment (strange situation procedure) or behavioral development at 18 months were found. The authors note that increased use with age may reflect parents responding to infants’ self-regulation, which means the direction of effect is unclear. Maternal reports of crying and of leaving the baby to cry were the main measure. Parents in the study reported their own practices, and the study does not test any program for leaving newborns to cry.

The skeptical view for young infants. Douglas and Hill’s 2013 systematic review examined behavioral sleep interventions applied by parents to infants younger than six months. They argued that studies linking such interventions to benefit have three methodological constraints: they fail to identify and control for feeding difficulties, fail to distinguish the neurodevelopmentally different first and second halves of the first year, and use reductive analyses of complex interventions. They concluded that these strategies have not been shown to decrease crying, prevent later sleep or behavioral problems or protect against postnatal depression, and that applying them as population prevention strategies risks unintended outcomes including more problem crying, premature cessation of breastfeeding, worsened maternal anxiety and, if infants must sleep in a room separate from the caregiver, an increased risk of SIDS. The review’s SIDS statement is consistent with the AAP’s recommendation to room share (see Safe Sleep Recommendations: What Every Postpartum Doula Must Know). It is a critical review whose authors state their conclusions strongly, and other researchers interpret the evidence differently.

What this means for doulas

• Do not sleep-train newborns. The trials with the best data are in infants at least 6 months old, and for babies under 6 months the systematic review found no demonstrated benefit and potential harms. Newborns need night feeds and responsive care.
• Do not catastrophize or promise. The evidence for older babies does not show harm in the studied outcomes, but it also does not show that every family should do it or that methods work for every baby. Context, feeding, temperament and parental wellbeing matter.
• Stay out of method advocacy. A doula can describe what the research says. Which approach, if any, to use later is a family and pediatric-provider decision.
• Keep safe sleep non-negotiable. Any approach has to include a safe sleep space, and room sharing is recommended by the AAP for at least six months.
• Support parents’ rest instead. Practical night help may address what is really driving the question, which is often exhaustion. See Supporting Exhausted Parents While Maintaining Evidence-Based Safe Sleep Practices.

Putting the evidence into practice

1. Ask what is behind the question. Is the parent exhausted, worried about a friend’s advice or under work pressure?
2. Explain the age gap. “Most of the studies are in babies older than six months. For younger babies, researchers disagree and the evidence does not show benefit.”
3. Offer realistic expectations. Newborn waking is normal, as described in Why Newborns Wake Frequently at Night: The Biology of Infant Sleep, and sleep consolidates gradually.
4. Offer low-risk supports now. Daytime light, calm night feeds, a predictable wind-down and shared night shifts are reasonable, though none are tested as ways to speed newborn sleep.
5. Refer. If a baby’s sleep problems come with poor feeding, reflux symptoms, breathing concerns or the parent’s distress, the pediatric provider should be involved. Parents with persistent low mood or anxiety should contact their own clinician.

Limits and uncertainty

The trials are small to moderate, mostly in babies with parent-reported sleep problems older than 6 months, and rely on parent-reported measures with follow-ups that lost many families. The longitudinal study is observational. The systematic review about under-six-month infants is a critical analysis whose conclusions are contested, and not all of the responses were reviewed to it or later trials. Methods, ages, definitions of harm and cultural context differ, and the studies measured specific outcomes, not every possible effect on every child. This article draws on abstracts only. Nothing here is advice about whether a family should use any method.

The bottom line

Sleep training research shows short- and medium-term sleep benefits for older babies without detected long-term harm in the outcomes studied, while for babies under six months the evidence does not show benefit and critics warn of risks. For a postpartum doula the practical conclusion is simple: do not train newborns, describe the evidence honestly when asked, keep safe sleep first and focus on the family’s rest and responsive care in the early weeks.

Birth & Baby University’s For Doulas page brings together its postpartum doula training, recertification and mentorship for doulas who support families through the newborn weeks and early sleep questions. Confirm that any program meets your certifier’s, employer’s or state’s requirements before you enroll.

This article is for professional education. It is not medical, legal or tax advice. Check the standards of your certifying organization and the rules where you work. For concerns about a baby’s health, contact a pediatric provider or emergency services.

Sources and further reading

• Gradisar M, et al. Behavioral interventions for infant sleep problems: a randomized controlled trial. Pediatrics (2016). Read the source
• Price AMH, et al. Five-year follow-up of harms and benefits of behavioral infant sleep intervention: randomized trial. Pediatrics (2012). Read the source
• Bilgin A, Wolke D. Parental use of ‘cry it out’ in infants: no adverse effects on attachment and behavioural development at 18 months. Journal of Child Psychology and Psychiatry (2020). Read the source
• Douglas PS, Hill PS. Behavioral sleep interventions in the first six months of life do not improve outcomes for mothers or infants: a systematic review. Journal of Developmental & Behavioral Pediatrics (2013). Read the source

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