Parents have all heard, and personally experienced, how critical a good night's sleep is for their children. But new research suggests that the consistency of kids' bedtimes matters just as much for their developing brains as the number of hours they get.

Researchers in the U.K. analyzed data from more than 11,000 children whose families were asked about their bedtimes when they were 3, 5 and 7 years old. At age 7, the children were tested on reading, math and spatial skills.

Seven-year-old girls who did not have a regular bedtime scored lower on all three cognitive tests than girls who had consistent bedtimes, although there were no significant differences among boys.

The study also suggests that not adhering to a set schedule can have cumulative long-term effects. Children whose parents said that they had inconsistent bedtimes when they were 3 scored lower on reading, math and spatial tests at age 7. And children who had inconsistent bedtimes at more than one period showed more pronounced cognitive effects.

"We don't know for sure if it is the consistency or just getting enough sleep that is critical, as the two are inextricably linked," study co-researcher Amanda Sacker, a professor of epidemiology and public health at the University College London wrote in an email to The Huffington Post. Her findings were published in the "Journal of Epidemiology and Community Health" this week.

It is possible that not having a set bedtime is a reflection of "chaotic family settings," the researchers wrote. Children with late bedtimes -- anything after 9 p.m. -- as well as those with inconsistent bedtimes were more likely to skip breakfast or have a television in their bedroom, both of which can have a negative impact on learning and development.

"It's probably part of a bigger picture, which is that families who don't have a bedtime routine are also often families who are lax about other things, like nutrition or reading to their child," said Jodi Mindell, director of graduate psychology at Saint Joseph's University in Philadelphia, who specializes in pediatric sleep medicine. She cited a 2004 National Sleep Foundation poll that found that children who get more sleep are also more likely to be read to at night, which helps boost language and reading skills.

But having a consistent bedtime is extremely important for keeping the circadian rhythm functioning appropriately, which benefits the body as a whole, including the brain.

"We all have circadian clocks -- internal clocks driven by our schedules, driven by light and also driven by the release of melatonin," Mindell explained. "If you have a consistent schedule every day, the internal clock is set every day and melatonin peaks at the same time every day."

The new study only looked at the consistency of bedtimes five nights a week, not on weekends. However, Michael Breus, a clinical psychologist, diplomate of the American Board of Sleep Medicine (and a frequent HuffPost contributor), said that true consistency means the same bedtime seven days a week, give or take maybe 30 minutes on the weekend.

"I would tell you that in my estimation, the majority of parents have no idea how important sleep consistency is," he said. "It's not because they don't care. They haven't been told."

A second study published this week in the "Journal of Developmental & Behavioral Pediatrics" drew further attention to the importance of children getting good, quality sleep and enough of it. It found that 4-year-olds who slept less than 9 hours and 45 minutes a night had more problems with anger and aggression than children who got the most sleep, according to their parents.

The National Sleep Foundation recommends that children age 1 to 3 need 12 to 14 hours of sleep a day, while 3- to 5-year-olds typically need 11 to 13 hours, and 5- to 12-year-olds need 10 to 11 hours.

Though teaching children how and when to go to sleep can, at times, be challenging, sleep experts say it is a clear step that mothers and fathers can take to maximize their children's ability to learn.

"It's a really good, simple step for parents to take," Mindell said. "Having an early bedtime and a set bedtime is a great thing to do to establish structure."

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