I agree. Because students have too much spare time. During the spare time that they have they could be participating in sports, work on the yearbook, or serve on the student council. In the spare time they have they could be doing something negative and could get in a lot of trouble. The principle is trying to give them something positive to do in their spare time. They don't have to actually have to participate in sports or work on the yearbook, they can have extra work to do or they can study but that's not enough time to keep the busy during the whole day after school. If they participate in sports they'll have practice after school, then after practice they will most likely have homework. If they were to participate in the school council they may have to stay after school for meetings. The principal is trying to have the students busy at all times.