I asked Marc Weissbluth, a pediatrician at Northwestern University and the author of the best-selling Healthy Sleep Habits, Happy Child, about the discrepancy, and he says that crying-it-out can take a long time, but typically only if the parents “have the child's bedtime too late, or they're not napping the child, or they're doing intermittent reinforcement,” – i.e. they're going back in to soothe the child instead of truly letting them cry it out.
(Extremely overtired babies resist sleep training, and parents who soothe their babies during training reward the crying, giving them reason to do it again and again.) Fix these problems, Weissbluth says, and crying-it-out should work in three days.
It's not just Weissbluth saying this. When the American Academy of Sleep Medicine reviewed the literature on infant and child sleep training, it reported that in 17 out of 19 published studies, unmodified extinction – the clinical term for crying-it-out – effectively reduced bedtime resistance and the frequency of nighttime wakings, concluding that it “has a strong record of accomplishment.”
The two published clinical trials on graduated extinction, the technique popularized by sleep researcher Richard Ferber, which involves leaving your baby to cry for increasing periods of time (but not necessarily all night), was deemed successful, too, but it takes longer. None of the studies found side effects associated with sleep training.
In a 2012 randomized clinical trial, Australian researchers followed up with 173 6-year-olds who had been sleep trained as babies, some of whom with graduated extinction, and found that they were no different than non-sleep-trained 6-year-olds with regards to emotional development, psychological health, parent-child closeness, and parental attachment.
And it's not just that a short stint of sleep training isn't harmful – it could actually be beneficial. People tend to underestimate the importance of sleep, but it's absolutely crucial for healthy development, and longitudinal studies have suggested that sleep-deprived infants often go on to become sleep-deprived children. Sleep deprivation affects parts of the developing brain involved in regulating emotions and thinking logically.
The harm of sleep-deprivation
Kids who don't sleep well are also more likely to injure themselves. Sleep-deprived adults, as in parents who are up at all hours of the night tending to sleepless babies, are much worse at deciphering emotional cues and being emotionally expressive themselves – problems that could potentially threaten the parent-child attachment bond.
Several trials have also found that sleep training reduces the risk of maternal depression – by as much as a factor of three – which is (actually!) chronically stressful for kids; a 2009 study reported that infants of depressed moms were more likely to be anxious and socially disengaged than were infants of healthy moms.
Crying-it-out is not for every parent, I know. But desperate parents – or parents who just want to be done with the 2 a.m. wake up – should feel fine trying the method. It's not just that there's no evidence of harm in crying-it-out – there is some solid evidence of no harm.
When sleep training works, and research suggests it often does, it can provide long-term benefits for the entire family – giving babies the sleep they need to develop into healthy toddlers and giving parents the rest they need to be sensitive, confident and happy caregivers.
Moyer is a science writer living in Brooklyn, N.Y., and is DoubleX's parenting advice columnist.