It takes only three-quarters of an hour to do the damage. After about 45 minutes of media, children's grades, sleep, social skills, and emotional balance start to decline. After four hours, only 1 per cent of children in middle school receive A's in Mathematics and English Language Arts. And, after four hours of screen time, children take 20 times longer to fall asleep than children with limited media use. That's what the Learning Habit study has found after examining family routines in 46,000...