Over 11,000 children were involved in a longitudinal study that found irregular sleep schedules and frequent late nights resulted in worsening performance on tests of reading and mathematical abilities, researchers from the University College London reported Monday.

Featured in the Journal of Epidemiology and Community Health, the study examined children at ages three, five, and seven in order to track their academic performance in relation to their bedtimes. The study found children who had no regular bedtime or went to bed past 9:00 p.m. had lower scores for reading and math.

Girls who had no regular bedtime showed a greater detriment to their overall performance than boys who had no regular bedtime.

"The take-home message is really that routines really do seem to be important for children," said the study's lead researcher, Professor Amanda Sacker, who added that controlling for external factors such as unstable households and families, which can lead to poor performance even with a restful night's sleep, was something they considered.

"We tried to take these things into account," she said.

Children who had less stable households tended to be less socially advantaged and often watched TV late into the night, while children whose families had more rigid structure were often read to before bed.

Adjusting for these factors, the link between erratic bedtimes and poor performance held steady.

The team hypothesized about the impacts of an irregular sleep schedule on children, pinpointing a child's developing brain as the greatest player at risk. When a child doesn't receive the proper sleep at consistent intervals each night, the researchers concluded, his or her brain's ability to store new information becomes impaired.

Erratic bedtimes were most common at the age of three, when around one in five of the children went to bed at varying times, the BBC reports. By the age of seven, more than half the children had a regular bedtime of between 7:30 p.m. and 8:30 p.m.

Sacker said that bedtimes much earlier than 7:30 p.m. wouldn't necessarily add anything to a child's brain power.

In general, some experts are less reliant on the consistency and more concerned with the quality of the sleep once a child goes to bed.

"At first glance, this research might seem to suggest that less sleep makes children less intelligent, however, it is clearly more complicated than that," said Dr. Robert Scott-Jupp of the Royal College of Pediatrics and Child Health.

"While it's likely that social and biological brain development factors are inter-related in a complex way," he added, "in my opinion, for schoolchildren to perform their best, they should all, whatever their background, get a good night's sleep."

Sacker agreed, noting that when impaired brain function is at stake, parents should find comfort in taking any action at all.

"Establishing a good bedtime routine early in childhood is probably best," she said. "But it's never too late."

Source: Kelly Y, Kelly J, Sacker A. Time for bed: associations with cognitive performance in 7-year-old children: a longitudinal population-based study. Journal of Epidemiology and Community Health. 2013.