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The Science of Sleep Training: What Research Actually Shows

Sleep training is often discussed using strong opinions and emotional language. This page summarizes what peer-reviewed research shows about infant sleep, crying, attachment, and family outcomes. Each section addresses a commonly stated claim and compares it to the available scientific evidence.

Executive Summary

Common Claims

What Research Shows

“Sleep training harms attachment”

Long-term studies show no differences in attachment or emotional health. Learn More.

“Crying causes toxic stress”

Temporary stress responses do not predict long-term harm. Learn More.

“Babies can’t self-soothe”

Many infants demonstrate self-settling within the first months. Learn More.

“Sleep training only benefits parents”

Improved parental mental health is linked to better child outcomes. Learn More.

“There are long-term negative effects”

Follow-up studies show no lasting harm years later. Learn More.

“There is one right or wrong way to handle infant sleep”

Multiple behavioral approaches show effectiveness; no single method is established as “best." Learn More.

Bottom line: Decades of research do not support claims that sleep training is harmful to children or the parent–child relationship.

Claim #1: “Sleep training harms attachment”
Question: Does sleep training harm attachment?
Answer: No.

What the research shows

Attachment security is defined by a child’s confidence in a caregiver’s availability over time, not by the absence of distress in specific situations.

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A large body of attachment research summarized in Cassidy & Shaver’s Handbook of Attachment (2016) explains that secure attachment develops through repeated experiences of sensitive, responsive caregiving across infancy and childhood—not through uninterrupted emotional regulation at all moments.

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Direct evidence comes from a randomized controlled trial follow-up by Price et al. (2012), which assessed children five years after behavioral sleep interventions (including controlled comforting and camping out). The study found no differences between sleep-trained and non–sleep-trained children in:

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  • Attachment security

  • Emotional or behavioral health

  • Parent–child relationship quality
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Similarly, Gradisar et al. (2016) followed infants who underwent graduated extinction, bedtime fading, or no intervention and found no differences in attachment style at 12 months, despite significant sleep improvements in the intervention groups.

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These findings indicate that sleep training does not interfere with the processes that form secure attachment.

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Key peer-reviewed studies

Claim #2: “Letting a baby cry causes toxic stress”
Question: Does crying during sleep training cause harmful stress?
Answer: There is no evidence that it does

What the research shows

Stress responses in infants are typically measured using cortisol, a hormone that fluctuates in response to many normal experiences.

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The frequently cited study by Middlemiss et al. (2012) measured cortisol levels in mothers and infants during three nights of extinction-based sleep training. The researchers found elevated cortisol in both mothers and infants during the first two nights, with reduced crying and lower maternal cortisol by night three. Importantly, the study did not measure long-term outcomes and explicitly noted that physiological stress responses may normalize as infants learn to self-settle.

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Long-term outcome studies are critical when evaluating harm. In contrast to short-term cortisol measurements, Price et al. (2012) assessed children years later and found no differences in emotional regulation, attachment, or stress-related outcomes.

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Additionally, developmental crying research by Barr et al. (1991) and St James-Roberts (2006) shows that increased crying is a normal developmental phase and varies across cultures and caregiving styles, without evidence of long-term harm.

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Key peer-reviewed studies

Claim #3: “Babies stop crying because they give up, not because they’re calm”
Question: Do babies actually learn to self-soothe?
Answer: Evidence supports the development of self-settling.

What the research shows

Observational and video-based studies provide insight into infant sleep behavior independent of parental interpretation.

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St James-Roberts et al. (2015) used video recordings and parent reports to show that many infants as young as 5 weeks wake briefly at night and return to sleep without signaling. Infants who demonstrated early self-settling were more likely to sleep for longer stretches by 3 months of age.

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A longitudinal study by Burnham et al. (2002) followed infants from birth to one year and found that greater self-soothing at 12 months was associated with:

  • Less time spent out of the crib during the first year

  • Longer response times to night awakenings at 3 months
     

These findings suggest that reduced signaling reflects developing sleep regulation skills, not emotional withdrawal.

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Key peer-reviewed studies

Claim #4: “Sleep training only benefits parents, not babies”
Question: Does sleep training benefit infants as well?
Answer: Yes.

What the research shows

Infant sleep quality is linked to emotional regulation and daytime functioning.

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Ross & Karraker (1999) found that sleep-deprived infants were more emotionally reactive and less capable of coping with stimulation than well-rested infants. While this study did not examine sleep training directly, it demonstrates the functional importance of sleep for infants.

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Parental well-being is also a key pathway. Dennis & Ross (2005) followed 505 mothers postpartum and found that infant sleep problems were strongly associated with maternal fatigue and the development of depressive symptoms within the first eight weeks. Maternal depression itself is a known risk factor for adverse child outcomes.

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Intervention studies such as Hiscock et al. (2007) showed that behavioral sleep interventions improved both infant sleep and maternal mental health, with benefits sustained months later.

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Key peer-reviewed studies

Claim #5: “There are long-term negative effects of sleep training”
Question: Are there lasting negative outcomes?
Answer: No evidence suggests that there are.

What the research shows

Few studies assess long-term outcomes, but those that do consistently find no harm.

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The Price et al. (2012) randomized trial followed children five years after sleep training and found no differences in:

  • Emotional health

  • Stress regulation

  • Physical health

  • Attachment
     

Similarly, Gradisar et al. (2016) found no differences in emotional or relational outcomes at 12 months between intervention and non-intervention groups.

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To date, no peer-reviewed study has demonstrated long-term harm associated with evidence-based sleep training methods.

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Key peer-reviewed studies

Claim #6: “There is one right or wrong way to handle infant sleep”
Question: Is there a single best method supported by science?
Answer: No.

What the research shows

A comprehensive review by Mindell et al. (2006) analyzed 52 studies involving over 2,500 participants and found that multiple behavioral approaches—graduated extinction, bedtime routines, scheduled awakenings, and parental education—were effective in reducing night wakings and bedtime problems.

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Another review by Kuhn & Elliott (2003) concluded that while further research is needed, existing evidence does not support claims that commonly used behavioral sleep interventions are harmful.

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Key peer-reviewed studies

  • Mindell, J. A., et al. (2006). Behavioral Treatment of Bedtime Problems and Night Wakings in Infants. Sleep.
    https://doi.org/10.1093/sleep/29.10.1263

  • Kuhn, B. R., & Elliott, A. J. (2003). Treatment efficacy in behavioral pediatric sleep medicine. Journal of Psychosomatic Research.
    https://doi.org/10.1016/S0022-3999(02)00429-5

  • Kerr, S. M., et al. (1996). Preventing sleep problems in infants. Journal of Advanced Nursing.
    https://doi.org/10.1046/j.1365-2648.1996.25721.x

  • Ramos, K. D., & Youngclarke, D. M. (2006). Parenting advice books about child sleep. Sleep.
    https://doi.org/10.1093/sleep/29.12.1616

Appendix: Full Reference List

 

This appendix contains all peer-reviewed studies and sources referenced on this page. Studies are grouped by topic for ease of review. All links point to the original journal publication or publisher page.

 

Attachment

  • Anisfeld, E., Casper, V., Nozyce, M., & Cunningham, N. (1990). Does Infant Carrying Promote Attachment? An Experimental Study of the Effects of Increased Physical Contact on the Development of Attachment. Child Development, 61(5), 1617–1627. https://doi.org/10.2307/1130769

  • Cassidy, J., & Shaver, P. R. (2016). Handbook of Attachment: Theory, Research, and Clinical Applications. Guilford Press. https://www.guilford.com/books/Handbook-of-Attachment/Cassidy-Shaver/9781462525292

  • Price, A. M. H., Wake, M., Ukoumunne, O. C., & Hiscock, H. (2012). Five-Year Follow-up of Harms and Benefits of Behavioral Infant Sleep Intervention: Randomized Trial. Pediatrics, 130(4), 643–651. https://doi.org/10.1542/peds.2011-3467

  • Gradisar, M., Jackson, K., Spurrier, N. J., Gibson, J., Whitham, J., Williams, A. S., & Kennaway, D. J. (2016). Behavioral Interventions for Infant Sleep Problems: A Randomized Controlled Trial. Pediatrics, 137(6). https://doi.org/10.1542/peds.2015-1486

 

Infant Crying and Stress

  • Barr, R. G., Konner, M., Bakeman, R., & Adamson, L. (1991). Crying in !Kung San Infants: A Test of the Cultural Specificity Hypothesis. Developmental Medicine & Child Neurology, 33(7), 601–610. https://doi.org/10.1111/j.1469-8749.1991.tb14930.x

  • Papoušek, M., & von Hofacker, N. (1998). Persistent Crying in Early Infancy: A Non-Trivial Condition of Risk for the Developing Mother–Infant Relationship. Child: Care, Health & Development, 24(5), 395–424. https://doi.org/10.1046/j.1365-2214.2002.00091.x

  • Radesky, J. S., Zuckerman, B., Silverstein, M., Rivara, F. P., Barr, M., Taylor, J. A., Lengua, L. J., & Barr, R. G. (2013). Inconsolable Infant Crying and Maternal Postpartum Depressive Symptoms. Pediatrics, 131(6), e1857–e1864. https://doi.org/10.1542/peds.2012-3316

  • St James-Roberts, I. (2006). Infant Crying and Sleeping in London, Copenhagen and When Parents Adopt a “Proximal” Form of Care. Pediatrics, 117(6), e1146–e1155. https://doi.org/10.1542/peds.2005-2387

  • Middlemiss, W., Granger, D. A., Goldberg, W. A., & Nathans, L. (2012). Asynchrony of Mother–Infant Hypothalamic–Pituitary–Adrenal Axis Activity Following Extinction of Infant Crying Responses. Early Human Development, 88(4), 227–232. https://doi.org/10.1016/j.earlhumdev.2011.08.010

 

Infant Sleep Development and Outcomes

  • Henderson, J. M. T., France, K. G., Owens, J. L., & Blampied, N. M. (2010). Sleeping Through the Night: The Consolidation of Self-Regulated Sleep Across the First Year of Life. Pediatrics, 126(5), e1081–e1087. https://doi.org/10.1542/peds.2010-0976

  • Hysing, M., Harvey, A. G., Torgersen, L., Ystrom, E., Reichborn-Kjennerud, T., & Sivertsen, B. (2014). Trajectories and Predictors of Nocturnal Awakenings and Sleep Duration in Infants. Journal of Developmental & Behavioral Pediatrics, 35(5), 309–316. https://doi.org/10.1097/DBP.0000000000000064

  • Burnham, M. M., Goodlin-Jones, B. L., Gaylor, E. E., & Anders, T. F. (2002). Nighttime Sleep-Wake Patterns and Self-Soothing from Birth to One Year of Age. Journal of Child Psychology and Psychiatry, 43(6), 713–725. https://doi.org/10.1111/1469-7610.00087

  • St James-Roberts, I., Roberts, M., Hovish, K., & Owen, C. (2015). Video Evidence That London Infants Can Resettle Themselves Back to Sleep After Waking in the Night. Journal of Developmental & Behavioral Pediatrics, 36(5), 324–329. https://doi.org/10.1097/DBP.0000000000000166

 

Parental Sleep, Mental Health, and Family Well-Being

  • Ross, C. N., & Karraker, K. H. (1999). Effects of Fatigue on Infant Emotional Reactivity and Regulation. Infant Mental Health Journal, 20(4), 410–428. https://doi.org/10.1002/(SICI)1097-0355(199924)20:4<410::AID-IMHJ6>3.0.CO;2-T

  • Dennis, C.-L., & Ross, L. (2005). Relationships Among Infant Sleep Patterns, Maternal Fatigue, and Development of Depressive Symptomatology. Birth, 32(3), 187–193. https://doi.org/10.1111/j.0730-7659.2005.00368.x

  • Bayer, J. K., Hiscock, H., Hampton, A., & Wake, M. (2007). Sleep Problems in Young Infants and Maternal Mental and Physical Health. Journal of Paediatrics and Child Health, 43(1–2), 66–73. https://doi.org/10.1111/j.1440-1754.2007.01005.x

  • Hiscock, H., Bayer, J., Gold, L., Hampton, A., Ukoumunne, O. C., & Wake, M. (2007). Improving Infant Sleep and Maternal Mental Health: A Cluster Randomised Trial. Archives of Disease in Childhood, 92(11), 952–958. https://doi.org/10.1136/adc.2006.099812

  • Hiscock, H., Bayer, J. K., Hampton, A., Ukoumunne, O. C., & Wake, M. (2008). Long-Term Mother and Child Mental Health Effects of a Population-Based Infant Sleep Intervention. Pediatrics, 122(3), e621–e627. https://doi.org/10.1542/peds.2007-2089

  • Wake, M., Morton-Allen, E., Poulakis, Z., Hiscock, H., Gallagher, S., & Oberklaid, F. (2006). Prevalence, Stability, and Outcomes of Cry-Fuss and Sleep Problems in the First Two Years of Life. Pediatrics, 117(3), 836–842. https://doi.org/10.1542/peds.2005-0775

 

Relationship Quality and Child Outcomes

  • Meijer, A. M., & van den Wittenboer, G. L. H. (2007). Contribution of Infants’ Sleep and Crying to Marital Relationship of First-Time Parent Couples. Journal of Family Psychology, 21(1), 49–57. https://doi.org/10.1037/0893-3200.21.1.49

  • James, S. L., Nelson, D. A., Jorgensen-Wells, M. A., & Calder, D. (2021). Marital Quality Over the Life Course and Child Well-Being. Development and Psychopathology. https://doi.org/10.1017/S0954579421000122

 

Sleep Training Methods and Evidence Reviews

 

This appendix is provided for transparency and verification. Inclusion of a study does not imply endorsement of a specific parenting philosophy, only that the study contributes data relevant to infant sleep, caregiving, or family outcomes.

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