The consistency of a young child's bedtime has been linked with positive performance on a variety of intellectual tests. The study was recently published in the Journal of Epidemiology and Community Health.
Researchers looked at information about bedtimes and standardized test scores for more than 11,000 children in the United Kingdom. The children were three, five, and seven years old. The research included regular surveys and home visits and questions for parents about bedtimes and other family routines. Children also took standardized tests in math, reading and spatial abilities when they were 7 years old.
The study found that, in general, consistent bedtimes were linked to better performance across all subject areas. This was especially true for 7-year-old girls, regardless of socioeconomic background - they tended to do worse on all three intellect measurements if they had irregular bedtimes. Boys in this age group did not show the effect.
Researchers found that, in general, children who had irregular bedtimes or went to bed after 9 p.m. tended to come from lower socioeconomic backgrounds than other study participants.
The study used a large group of participants but still only draws correlations, not causes. It is not proof that irregular sleep is a direct driver of lower test scores.