I know I had plenty of recess and still learned plenty. Kids are psychologically designed to sit in a classroom for eight hours straight. For that matter, neither am I. There are not words for how much better I would learn in veterinary school if I had some light in my classroom, or the opportunity to go play outside for a few minutes instead during the day.

Drilling more information into a child's head does not magically make the child acquire it. If the kid is jumping around in its seat, or antsy to get out of class just so he can go run around, he's not going to achieve what he needs to. You might believe that it's not too much to ask for a child to sit for eight hours so he can go run around at home. Go spend a few months sitting and observing in a first grader's classroom, then come back to me.

Specifically towards weight gain in children, how does this NOT make sense? Weight is a balance between energy intake AND energy use. A kid who has no recess at school, then comes home, does homework, and then plays video games all day or some other sedentary activity like many children these days do, will not burn many calories.