Sleep training — the process of modifying infant and toddler sleep behaviour — is one of the most debated topics in parenting. It generates strong feelings on all sides, and the debate is often more ideological than evidence-based. Understanding what the evidence actually shows about the main approaches, what they involve, and what the long-term research shows helps parents make a genuinely informed decision about what approach, if any, is right for their family.
The evidence is clearer than the public debate suggests: behavioural sleep interventions work, their short-term effects are well documented, and multiple long-term follow-up studies have found no harm to attachment, stress regulation, or development. This does not mean every family should sleep train; it means the decision can be made on grounds of family values, temperament, and circumstances rather than fear of harming the child.
Healthbooq supports parents in understanding their options for improving infant and toddler sleep, with guidance grounded in current evidence.
The Main Approaches
Extinction ("cry it out") involves placing the baby in the cot awake and not returning until morning (or until a set time), allowing the baby to settle independently. It is the most effective and fastest approach, but also the most difficult for parents to implement because it involves tolerating sustained crying.
Graduated extinction (Ferber method, "controlled crying") involves placing the baby in the cot awake and returning at progressively increasing intervals (for example, after three minutes, then five, then ten, extending the intervals over successive nights) to briefly reassure the baby without picking them up or feeding them. The reassurance prevents the most sustained crying of full extinction while still allowing the baby to learn to settle independently.
Camping out or chair method involves the parent sitting in the room (initially next to the cot, then progressively further away over nights to weeks) while the baby settles to sleep without being picked up or fed. It is slower and requires more parental consistency but involves less crying.
Bedtime fading involves gradually moving bedtime later until the baby is naturally falling asleep earlier (exploiting sleep pressure to improve sleep onset) and then moving the bedtime earlier as sleep improves. It addresses sleep timing and onset without focusing on independent settling.
Bedtime routine optimisation — a consistent, calming sequence of pre-sleep activities (bath, feed, book, song, bed, same every night) — is not strictly "sleep training" but is the foundation for all other approaches and has its own evidence of benefit for settling time and overnight waking.
What the Evidence Shows
The largest and most methodologically rigorous research in this area includes a randomised controlled trial by Hiscock et al. (2007) and a five-year follow-up by Price et al. (2012), which found that infants whose parents received behavioural sleep intervention showed the same attachment security, emotional development, and cortisol (stress) profiles as control infants at five years. No harm was detected at any timepoint.
Multiple other studies have found no evidence of harm to emotional wellbeing, cognitive development, or parent-child relationship from behavioural sleep interventions. The concern that "cry it out" methods cause lasting damage through elevated cortisol or compromised attachment is not supported by the current body of evidence.
Sleep deprivation in parents — the most consistent consequence of infant sleep disruption — is associated with postnatal depression, reduced parenting responsiveness, relationship strain, and occupational impairment. Improving infant sleep reduces these risks for parents.
Readiness and Timing
Most paediatric sleep guidelines suggest that behavioural sleep interventions are appropriate from around six months, when the baby's neurological and physiological development supports independent sleep consolidation. Before six months, supporting the baby to sleep (feeding, rocking) is appropriate and expected; after six months, it is a choice, not a necessity.
Key Takeaways
Behavioural sleep interventions for infants and toddlers — including graduated extinction ('controlled crying') and extinction ('cry it out') — have a substantial evidence base showing effectiveness for improving sleep without detectable short or long-term harm to attachment, stress regulation, or development. They are not the only option and they are not right for every family. Fading methods, bedtime routine optimisation, and addressing sleep associations can also be effective with less distress. The decision about how to approach infant and toddler sleep is a family decision; the evidence base informs that decision but does not prescribe it.
