Parents often worry about their children’s screen time, and for good reason. A new study shows that too much screen time can result in poor sleep patterns, struggles in school and combative behavior.

A study published in JAMA Pediatrics shows that children enjoy more sleep, do better in school and reap other health benefits when parents monitor just how much time their kids spend in front of the TV, on the computer or on their phones and tablets.

Iowa State University psychology professor Douglas Gentile, who was lead...