Why do I like reading more in the summer than during school?

Usually at the beginning of the summer I pick out certain books to read; I read at least four or five books every summer. But then once school starts I try to stay away from books as much as I can. I think this is because during the summer I am free to read what I want, when I want to read and read the book for how ever long I want to. In school we are practically forced to read everyday or a certain amount of pages a semester. I hate that feeling, the feeling of being compelled to do something you loved to do. It is weird to think that I liked to read, but yet I don't read as much or enjoy reading during the school year. The thing is that sometimes it is hard to find time to read or even a desire to read right after school, where we've been reading all day. It is hard to find the yearning to pick up a book and waste the rest of your day that has already mostly been spent on school reading other things.