The sleep training debate is a passionate one, with many citing research to back their claims. Unless you have the drive to read through all of the research yourself, it can sound like the science backs both those opposed and those in support equally. It can be distressing to a parent, who genuinely wants to do what’s best for his or her child. Will sleep training harm your baby?

First, let’s look at the research on sleep training that offers evidence that it may be harmful.


Really. There is none.

So what are opponents of sleep training using to back their claims? Here are four of the most common arguments and the studies being used to support them.

  1. It’s important to respond immediately to a baby’s cries.

In a widely-circulated article on Psychology Today warning of the dangers of crying it out, author Darcia Narvaez claims, “The fact is that caregivers who habitually respond to the needs of the baby before the baby gets distressed, preventing crying, are more likely to have children who are independent than the opposite (e.g., Stein & Newcomb, 1994).”

If you look at the reference she cites though, it’s more than a little puzzling. It doesn’t even address responding to a baby’s cry. In Stein & Newcomb’s research, titled, “Children’s Internalizing and Externalizing Behaviors and Maternal Health Problems,” participants consisted of mothers who had at least one child between the ages of 2 and 10, and their children in that age bracket. Children under the age of 2 were actually excluded from this study, making it impossible to use this reference to support a claim that parents should quickly respond to their baby. Additionally, the researchers were looking at whether maternal health issues, such as depression and physical illness, had an effect on the behavior of their children as they grew. The study had absolutely nothing to do with crying.

How does responding immediately to baby’s cries affect sleep?

There is no doubt that babies depend on a parent responding sensitively to their cries. Does that mean that more response is better?

In one interesting study, two researchers observed mothers’ response to baby’s crying in 50 Dutch lower- to middle- class families over baby’s first 15 months.

The researchers in this study surprisingly observed that, “prompt responses not only led to more crying later in the first year of life, but were also associated with insecure-avoidant attachments.” According to research on this style of attachment, insecure-avoidant children have learned that their communication efforts do not influence their mother’s response. This makes sense if the mother is not trying to understand what her child’s cries mean: mom simply responds to every cry to make the crying stop.

The authors note that mothers who differentiate between cries of severe versus moderate distress are able to consistently respond to the former. They allow the baby to learn to manage small levels of distress when the mother does not immediately respond to the latter, intense cries. In this way, the authors theorize, a baby is able to learn how to communicate to receive necessary care, and also how to adapt to mild stress.

When it comes to sleep, that careful balance of responsiveness with an inquisitive pause to see what baby is communicating can make an enormous difference. Professor of Child Psychology Ian St James-Roberts studied three groups of parents: one group from London, where many parents follow a parent-led, scheduled approach to newborn care; one group that expressed an intent to follow a “proximal care” style of parenting, or what some might compare to popular forms of attachment parenting (holding baby for at least 80% of the waking day, frequent breastfeeding, and rapid response to cries); and a third group from Copenhagen who followed a more middle-of-the road approach, holding their baby more often than the London parents but much less than the proximal care parents.

The results of the study were striking. The London “parent led” infants cried the most of all three groups, though all three sets of infants experienced a decrease in crying by 12 weeks of age. The proximal care infants, although they cried the least, were also the least likely to be sleeping for 5 consecutive hours at night by 12 weeks of age. But the Copenhagen babies, with the balanced style of parenting, had a lower level of crying similar to the proximal care babies, but also enjoyed the longer stretches of sleep at 12 weeks like the London babies. Responsive, yet respectful.

  1. Excessive crying harms a baby’s development.

In citing a reference to support his claim for what is known as “cry-it-out” (CIO) causing, “decreased intellectual, emotional, and social development,” Dr. Sears says, “Researchers at Pennsylvania State and Arizona State Universities found that infants with excessive crying during the early months showed more difficulty controlling their emotions and became even fussier when parents tried to console them at 10 months.” (Stifter & Spinrad, 2002).

In the study he’s referring to, “The Effect of Excessive Crying on the Development of Emotion Regulation,” 116 participants filled out cry diaries when their infants were six weeks old. Six weeks. Nobody is sleep training at six weeks. This study didn’t even have anything to do with sleep. This study was looking at how much crying these babies did at an age known to be the peak for crying and fussy behavior. Researchers then tracked how the babies developed.

When the infants were 5 and 10 months old, they participated in a laboratory follow-up where researchers observed baby’s reactions during a series of procedures. They were curious about how colicky babies developed emotional control. How baby developed was not a reflection of a mother ignoring her baby’s cries as Sears suggests. Nobody in this study was ignoring any cries. Additionally, the researchers found that having a more sensitive mom early on did not predict greater self-control later on for these colicky infants. Sensitive moms care for their babies when they cry. But you don’t have to carry the weight of believing that if you tried harder or cared more, that you could give your child a different character quality.

So what does sleep training research tell us about letting a baby cry?

An Australian group of researchers published a five-year follow-up of a randomized, controlled clinical trial of sleep training intervention (Price, 2012). Participants received health care at centers that had been randomized as to whether the nurses were trained to offer sleep training advice, while others were reserved as the control centers with nurses who gave general advice in regards to sleep. It’s not a super conclusive way to create a test and a control group, but ethically it’s difficult to randomly assign families sleep train or not to sleep train long-term. When the children were tested near the time of their sixth birthday, the results of cortisol sampling (as a measure of stress) and an assessment of attachment showed no evidence of harm as a result of sleep training.

A study published in 2016 in the journal Pediatrics looked at a randomized, controlled clinical trial of 43 infants who were placed in either a graduated extinction (a modified form of CIO) group, a bedtime fading group (bedtime was temporarily delayed to make it easier for baby to fall asleep, then moved earlier again), or a control group (Gradisar, 2016). Families were allowed to change the group they were assigned to. One week into the experiment, both the graduated extinction infants and the faded bedtime ones had a much quicker time to fall asleep than the control group, and both were waking less frequently. Cortisol samples were taken at one week, one month, and three months, showing what the authors describe as “small-to-moderate” decreases for the two test groups compared to the control group. At 12-months follow-up, no differences were found between the three groups in terms of attachment styles.

  1. Cry-it-out is harmful to the parent-child relationship.

Frequently used to support this argument is the 2012 Middlemiss study. In this experiment 25 mother-infant pairs spent three days at a residential, hospital-based location in New Zealand. Nurses put the infants to sleep in cribs in a room apart from their mothers, where the babies were allowed to cry until they fell asleep. By night three, all were falling asleep on their own with minimal crying. Saliva cortisol samples were collected from both the mothers and the infants before and after bedtime on the first and third day.

The infants’ saliva cortisol levels stayed at the same level throughout the entire experiment. The mothers’ cortisol levels matched the babies’ levels on the first night. By the third night, when the babies were no longer crying at bedtime, the mothers’ cortisol levels had dropped, while the babies’ still had high levels. This difference between the babies’ and mother’s stress is where the concern comes in. Middlemiss emphasizes the importance of mothers being in tune with their infant’s level of distress.

There are a few problems here though. The biggest one being, there was no control group. Were the babies’ cortisol levels high just because they were in a new environment, or because it was a stranger putting them to bed? Would cortisol levels have dropped if the same experiment was done in homes with the mothers putting the infants to bed awake? We don’t know. Additionally, it appears from the data that not every infant and every mother was included in each saliva testing, without any reason given as to why. 17 mothers out of the 25 were tested on the first night, but only 12 mothers tested on the third night. That’s less than half of the maternal participants, and a significant piece of the argument that Middlemiss is trying to make.

There’s actually more evidence that sleep training benefits the parent-child relationship.

Using an established scale to measure security, a study of 35 infants with sleep problems found that after unmodified extinction (cry-it-out), the children’s security and likability increased, and their emotionality and tension decreased. Another study of 95 children with sleep struggles found that prior to sleep training, these children were rated as more insecure than a matched comparison group. After sleep training, not only did sleep improve, but so did the children’s daytime behavior and the family’s well-being–and the difference in security from the comparison group disappeared. Mothers in particular reported feeling less tired, depressed, and discouraged afterward. Happier babies, happier moms.

  1. Frequent waking in early childhood is something normal that we should just expect.

Certainly babies need to wake often in their first few weeks and months of life. Some critics have suggested that continued waking beyond this period is still natural though, and the perception that needs to change is the parents’, not the child’s behavior.

On her blog Evolutionary Parenting, in a post titled, “Myths and Facts About Night Waking,” Tracy Cassels refers to a longitudinal study of 1,200 children saying, “At 3 years of age, 25.6% of toddlers were waking and signalling their parents 3 or more nights per week. And notably, none of these children suffered any clinical problems or sleep disorders.” (Weinraub, 2012)

Well, no. These children don’t have any clinical problems, because in most cases, the cause of continued night waking is behavioral.

When it comes to expectations, believing that your baby is capable might be the more fruitful approach.

A group of first-time Israeli mothers were recruited during pregnancy. They were asked to rate their response to a number of scenarios of an infant or young child waking at night. Before these women even had even given birth, their mindset played a significant role in how well their own baby slept. Those who were more willing to set reasonable limits in the fictional scenarios were also the mothers who had babies sleeping for longer periods of time at 6 months of age.

The researchers observed, “When mothers put more emphasis on infant distress and need for help in their interpretations of infant sleep problems and night wakings, then parents were more likely to be actively involved during bedtime and at night. These soothing variables were significantly correlated with more disrupted infant sleep.” Simply put, the mothers’ way of thinking, even before their babies were born, significantly predicted how well their own child would sleep.

A follow-up study continued to find similar results as the children grew older. Mothers who expressed difficulty setting limits when their child was 12 months old were significantly more likely to have bedtime and/or night waking problems with their child three years later.

Bottom line? There simply is no evidence that sleep training will harm your baby. On the contrary, getting a healthy amount of sleep benefits the whole family. Decide for yourself if sleep training is the right step for you. If you do choose to sleep train, rest assured that in the context of a loving, responsive home, you are giving your child healthy habits that will last a lifetime.

I'm ready for a good night's sleep