@Sneakers41 - I think that kids are becoming more sedentary with the growth of technology. When I was a kid we always went outside to play and I always got good grades.
But a lot of kids now come home and go to their computer, play video games, or watch television all day. My kids have to do their homework before they get to play and when they play video games it is always a fitness or dance oriented game that will get them sweating.
They also don’t watch television during the week only on weekends. You would be surprised how much your children can do when they don’t watch television. They also have time to read and they concentrate better on their homework.