You’ve always known the kids should be in bed at a reasonable hour. It’s good for growing bodies… and for moms’ and dad’s sanity. And although you might not have had a real scientific reason why, now there is some solid proof.

In a study recently presented at SLEEP 2010, the twenty-fourth annual meeting of the Associated Professional Sleep Societies, researchers found that children score higher on several types of developmental tests when they abide by bedtime rules and when they get ample sleep.

In the largest study of its kind, data from about eight thousand four-year-olds was analyzed through developmental assessments as part of the Early Childhood Longitudinal Study. Information was obtained via parent phone interviews when each child was nine months old and again when they turned four.

When it comes to sleeping habits, having a usual bedtime was directly tied to scoring higher on all of the cognitive measurement tests. Children whose parents had hard and firm rules about bedtime curfews were rewarded with higher scores in categories that focused on things like receptive and expressive language, reading, writing and early math abilities. And the earlier the bedtime the better. Researchers noted that children who hit the hay sooner also scored higher on most developmental tests.

The American Academy of Sleep Medicine recommends preschool children get a minimum of eleven hours of sleep each night. That might seem like a lot of logs to saw, but experts say substantially less sleep can have negative consequences for development and school achievement. The news should come as a wakeup call for moms and days everywhere: Keeping up with a standard bedtime… and an early one… reaps its rewards, for kids and parents alike.