Parents know a nightly bedtime is not always easy to enforce. But researchers say bedtime rules may improve a child's development.

A new study found better results in four-year-olds who go to bed around the same time every night and sleep at least eleven hours. Getting less than that was linked to lower abilities in language, reading and early math skills.
Researchers at SRI International in California did the study. It involved about eight thousand preschool children whose parents took part in government research on early childhood.