Pregnancy and child

Irregular bedtimes make children 'naughtier'

“Children with regular bedtimes less likely to misbehave, research shows,” The Guardian reports. The advice is prompted by a new study into the effects of irregular bedtimes on children’s behaviour.

The researchers studied more than 10,000 children whose behaviour and bedtime patterns were monitored when they were aged three, five and seven years.

It found children who had non-regular bedtimes had more behavioural problems over the years than those who had regular bedtimes. This was assessed using a validated mother- and teacher-completed behaviour questionnaire.

Encouragingly, the association between irregular bedtime and misbehaviour appears to be reversible. Many children with a previous history of ‘acting up’ experienced an improvement in behaviour once their bedtime patterns were better regulated.

One suggested explanation for the results was that those with non-regular bedtimes were getting less sleep. This could, potentially, affect the development of regions of the brain associated with behaviour regulation. However, they didn’t measure sleep directly so this remains an assumption.

This study alone cannot prove that other factors aside from bedtime patterns weren’t also influencing behaviour. Child behaviour is an incredibly complex area and many factors have the potential to affect it.

With these limitations in mind, setting a regular bedtime schedule is thought by most childcare experts to be an effective method of making sure your child gets the right amount, and improves the quality, of sleep.

Read more Healthy sleep tips for children.

Where did the story come from?

The study was carried out by researchers from University College London and was funded by a grant from the UK Economic and Social Research Council.

The study was published in the peer-reviewed medical journal Pediatrics.

Overall the media reporting of the study appeared accurate. Though the inherent limitation of the study – the fact that other, unaccounted for, factors may have been influencing behaviour (confounders) was not discussed.

What kind of research was this?

This was a cohort study measuring bedtime information and behavioural difficulties of the same group of children over a period of four years.

The study reported that the causal links between disrupted sleep and behavioural problems are not clear. So their study aimed to address the issue by answering the following questions:

  • Are bedtime schedules associated with behavioural difficulties?
  • Do effects of bedtime schedules on behaviour build up over early childhood?
  • Are changes in bedtime schedules linked to changes in behaviour?

A cohort study is useful for measuring changes over time, such as the impact of changes in bedtime patterns and behaviour. Limitations of this approach are discussed in the conclusions section.

randomised control trial would be a more effective way to assess the impact of bedtime patterns on behaviour but this would be problematic to perform for practical and ethical reasons.

What did the research involve?

Information from 10,230 seven-year-olds from the UK Millennium Cohort Study was analysed – this is an on-going cohort study involving children born around the turn of the millennium. Bedtime information was collected at three, five and seven years, alongside behavioural difficulties scores as rated by mothers and teachers.

At three, five and seven year time points the child’s mother was asked, “On weekdays during term-time, does your child go to bed at a regular time?” (response categories were always, usually, sometimes, and never). These were then categorised into either “regular bedtime” (always or usually) or “non-regular bedtime” (sometimes or never) for analysis. Questions were not asked about bedtimes on weekends.

Behavioural difficulties were assessed by teachers and mothers who were asked to complete a validated questionnaire called the Strengths and Difficulties Questionnaire (SDQ), age four to 15 years version.

The SDQ asks questions about five domains of social and emotional behaviour, namely conduct problems (or in layman’s terms “being naughty”), hyperactivity, emotional symptoms, peer problems, and prosocial behaviour (behaviour intended to benefit others).

Scores from the first four domains are combined to construct a total difficulties score.

Children with attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder were excluded from the study.

The analysis took into account observed reductions in behavioural difficulties scores as children get older, alongside numerous other potentially influential factors, known as confounders, such as household income, highest parental education, birth order of the child and psychological distress experienced by the mother.

What were the basic results?

In describing the study cohort the authors noted that children without regular bedtimes and those with later bedtimes (9 PM or later) had more socially disadvantaged profiles. For example, they were more likely to be from the poorest homes, have parents without degree level qualifications, and have mothers with poorer mental health. This was later adjusted for in the statistical analysis.

The main findings were:

  • There was an incremental worsening (“dose-dependent”) in behavioural scores the longer children were exposed to non-regular bedtimes. Behavioural scores got worse compared to those with regular bedtimes as they progressed through age three, to age five to age seven. The behavioural deterioration was reported by both mothers and teachers.
  • Children who changed from non-regular to regular bedtimes had statistically significant improvements in behavioural scores, changes that were described as “nontrivial” by the study authors.
  • For children who changed from regular to non-regular bedtimes between ages five and seven there was a statistically significant worsening in scores.

How did the researchers interpret the results?

The researchers’ main conclusions were that “having regular bedtimes during early childhood is an important influence on children’s behaviour” and that in light of the apparent reversibility of the bad effects “there are clear opportunities for interventions aimed at supporting family routines that could have important impacts on health throughout life”.


This large cohort study indicates that seven-year-old children with non-regular bedtimes have more behavioural difficulties, as reported by both mothers and teachers using a questionnaire, than children who had regular bedtimes.

There appeared to be a dose dependent relationship with the behaviour gap between regular and non-regular bedtimes widening as the children got older (from three to seven years old).

The behaviour-bedtime relationship appeared to be reversible in both directions as children who adopted new regular bedtimes improved behaviour and those who went from regular bedtimes to non-regular showed signs of deterioration.

There are a number of factors that need to be taken into account when considering the evidence provided by the researchers.


The study went to great lengths to adjust for common confounders that could account for differences in behavioural difficulties in children, other than potential lack of sleep due to irregular bedtimes.

Despite their efforts, as behaviour is influenced by so many factors, we cannot be sure that the differences observed are only due to bedtime patterns.

For instance, there may still be important factors, not measured in the study that have influenced these results, such as other unmeasured environmental and lifestyle habits. These could include the child’s diet and exercise, the type of games and other activities they take part in, use of electrical devices such as smartphones or tablets, number of people in the house, mental health history of the father, ethnic background and so on.

What constitutes a meaningful effect?

Another main consideration for this type of study is the magnitude of difference reported in behavioural difficulties between the regular and non-regular bedtime groups, and whether this is meaningful to the person or parents involved.

The study authors stated that a 0.9-point difference in behavioural scores would correspond to a small meaningful difference and that a 2.3-point difference would correspond to a moderate meaningful difference. Additionally, they reported a 1-point difference in behavioural difficulties scores has been shown elsewhere to predict clinically diagnosed problems. It is not clear if these definitions are accurate or whether the parents would agree that these changes were meaningful.

The magnitude of the behavioural differences shown in the study between the two bedtime groups ranged from 0.5 points to 2 points, so using the authors’ guide they appear to be small to moderately meaningful differences.

A change from non-regular to regular bedtimes between ages five and seven corresponded to a behavioural improvement of 1.02 points, suggesting many of the negative effects of non-regular bedtimes may be reversed.

The magnitude of a change from three years to seven years, was slightly less at 0.63 points.

Excluded groups

It should also be noted that none of the children in this study had diagnosed problems such as ADHD, so it is unclear what effect bedtime patterns would have on children with these sorts of chronic conditions.

Loss to follow-up

The study lost touch with approximately 12% of participants in the original cohort. They took reasonable steps to address this missing information in the analysis so this is unlikely to be a source of bias.


A further potential limitation is that the study did not record sleep quality or quantity directly (they used regular bedtimes as a proxy measure for this) and relied on the recall of events by mothers. This may have led to recall bias based on expectations that a set bedtime is something a good mother should be doing. However, this would make it less likely to find differences between the two groups. 

The bottom line is that this study suggests there may be a link between non-regular bedtimes and increased behavioural difficulties, and proposed that lack of sleep was the likely causal link.

However, this study alone cannot prove that other factors weren’t also influencing the children’s behaviour or that non-regular bedtimes or lack of sleep were the main cause of the behavioural problems.

NHS Attribution