I believe it can be both: Helpful and harmful. Helpful as it gives you more practice to reinforce things such as maths. Harmful because so many hours have been spent at school concentrating on work and teachers, it can seem like extra after school is just overkill. Also, school involves a lot of sitting down, when out of school it would be healthier for the body to be moving around, engaging in exercise and other things. Humans weren't designed to be sedentary. However, in this day and age knowledge is very important hence why education has such an emphasis and why homework can be necessary at times.