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Sleep training attracts strong opinions. There is real anxiety on one side — "it's cruel to let them cry," "what about attachment?" — and real exhaustion on the other. Both are honest responses to the situation.
This article sets aside the emotional framing for a moment and looks at the numbers from RCTs and meta-analyses. The goal is less to answer "which method is right?" and more to clarify what each approach is actually doing, and under what conditions each tends to work.
How Common Is Infant Sleep Disruption?
Start with context. Frequent night waking and difficulty falling asleep are reported in 20–30% of children aged 0–3, making it one of the more prevalent concerns in early childhood [1]. The evidence base for behavioral sleep interventions was comprehensively reviewed by Mindell et al. in 2006.
Mindell 2006 Meta-Analysis — The Overall Picture
Mindell et al. synthesized 52 RCTs: randomized controlled trials; studies where participants are randomly assigned to treatment or control groups to measure causal effects and quasi-experimental studies on behavioral sleep interventions [1]. Key findings:
- Effect sizes: statistical measures of how large or meaningful an intervention's impact is; d = 0.8+ is considered large for sleep-onset interventions ranged from d = 0.84 to 1.06 (large effects)
- Significant improvements in both night wakings and sleep-onset latency
- Parents' mental health (depression, anxiety) also improved significantly
- No long-term adverse effects on child attachment or behavioral development were identified
This establishes that the category of behavioral intervention works. It does not tell us which specific method works best.
Comparing Three Approaches
Graduated Extinction (the Ferber Method)
Proposed by Richard Ferber in 1985 [5], this approach has the parent place the child in the bedroom and leave. The parent waits a set interval before returning — even if the child is crying — and gradually extends the interval over several nights.
Effect size: large; improvements are typically visible within days to a week of starting
Main challenge: responding to crying is emotionally demanding, and adherence is often the limiting variable. In the Hiscock and Wake RCT, whether parents could sustain the approach was the single most important predictor of outcome [2]
Unmodified Extinction (No-Cry Method)
The full version: no parental re-entry for crying, regardless of duration. Effects may appear fastest of the three methods, but the practical difficulty is also the highest.
Camping Out (Chair Method)
The parent stays in the child's room but gradually increases distance over several nights — beginning seated next to the child, then moving the chair progressively toward the door, eventually leaving.
Parental acceptability: the highest of the three
Time to effect: the longest of the three, often several weeks
The 2002 RCT by Hiscock and Wake found that across methods, "which specific method was used" mattered less than whether parents could implement it consistently [2].
"Does Letting Them Cry Harm Attachment?" — Long-Term Follow-Up
The most direct evidence comes from Price et al.'s five-year follow-up study [3]. Comparing families who used the Ferber method with those who did not, and assessing emotional development, behavioral outcomes, and the parent–child relationship at age five, the study found no statistically significant differences between groups (p > 0.05).
In Gradisar et al.'s 2016 RCT, cortisol: a stress hormone released by the adrenal glands; elevated chronically, it signals sustained physiological stress levels and attachment scores in children who underwent graduated extinction showed no significant differences from controls [4]. The concern that letting a child cry damages attachment is not supported by the current evidence base. That said, these studies have limitations — constrained follow-up periods, potential confounders — and it would be equally inappropriate to invoke them as proof that "there is definitively no problem."
The Bedtime Routine as a First Step
Before choosing a method, there is something to try. Mindell et al.'s 2009 RCT found that maintaining the same nightly routine — bath, gentle massage, picture book — for three consecutive weeks produced a 35% reduction in night wakings and a 17-minute reduction in sleep-onset latency, with significant improvement in parent mood as well [6].
A consistent 30–45-minute bedtime routine, tried first for three weeks, is a less invasive starting point before any formal sleep training begins.
Practical Takeaways
1. Consistency over method Implementing any given method perfectly matters less than applying whatever method is chosen consistently, every night. Hiscock and Wake's RCT emphasizes this throughout [2].
2. Try the bedtime routine first Three weeks of a consistent 30–45-minute routine is worth attempting before anything more structured. Many families see meaningful improvement at this stage alone.
3. Match the method to your current capacity The useful question is: "can I actually sustain this for three days?" A parent who is already exhausted and abandons the Ferber method after two nights is likely to see worse outcomes than one who runs Camping Out patiently for three weeks. Realistic capacity — today's capacity, not an idealized version — should determine the choice.
Tracking sleep changes in a log — number of night wakings, sleep-onset time, overnight feeding count — over several days makes the effect of any intervention easier to evaluate objectively.
Summary
Graduated extinction, unmodified extinction, and Camping Out all have evidence of effectiveness as behavioral sleep interventions. The five-year follow-up evidence does not support the concern that they damage attachment. What matters in practice is less which method is chosen, and more whether the bedtime routine is in place, whether the chosen method is applied consistently, and whether the caregiver can realistically sustain it.
References
- Mindell JA, Kuhn B, Lewin DS, Meltzer LJ, Sadeh A; American Academy of Sleep Medicine. Behavioral treatment of bedtime problems and night wakings in infants and young children. Sleep. 2006;29(10):1263–1276. doi:10.1093/sleep/29.10.1263. PMID: 17068979.
- Hiscock H, Wake M. Randomised controlled trial of behavioural infant sleep intervention to improve infant sleep and maternal mood. BMJ. 2002;324(7345):1062–1065. doi:10.1136/bmj.324.7345.1062. PMID: 11991909.
- Price AM, Wake M, Ukoumunne OC, Hiscock H. Five-year follow-up of harms and benefits of behavioral infant sleep intervention: randomized trial. Pediatrics. 2012;130(4):643–651. doi:10.1542/peds.2011-3467. PMID: 22966025.
- Gradisar M, Jackson K, Spurrier NJ, et al. Behavioral interventions for infant sleep problems: a randomized controlled trial. Pediatrics. 2016;137(6):e20151486. doi:10.1542/peds.2015-1486. PMID: 27221288.
- Ferber R. Solve Your Child's Sleep Problems. New York: Simon & Schuster; 1985 (revised ed. 2006).
- Mindell JA, Telofski LS, Wiegand B, Kurtz ES. A nightly bedtime routine: impact on sleep in young children and maternal sleep and mood. Sleep. 2009;32(5):599–606. doi:10.1093/sleep/32.5.599. PMID: 19480225.