Some of the activities after school could be very important to the person, and that person may want to succeed in what they are doing, and doing it in school can help them because when they go to competitions they can be seen and may get a scholorship. Also some activities make you wiser and healthier.
Many pupils enjoy extra curricular activities and I see no real reason to get rid of them. Hobbies outside of school are good to have. Yes, education is a priority at school but there is and should remain time for other things too. Music and art can be good forms of self expression. Sports are good for health as exercise is involved. Exercise is vital for health and can even aid improving one's focus in the classroom. And when you consider how many hours students spend sedentary at school, it is a good thing that after school sports exist.