This ariticle states that setting up rules for computer usage ahead of time helps to eliminate problems later. A lot of good suggestions that should start at a young age and continue to reinforce throughtout their schooling.
Ask some principals to identify the most difficult part of their day, and it will be recess, a time when fights and visits to the nurse's office skyrocket. But before you decide to eliminate this important opportunity for physical activity, consider the causes of the chaos.