it's normal problem for everyone, you don't worry about it. First, before going to bed, you should check school timetable everyday and put your book that you will study tomorrow in the bag. You ought to focus on study more. I think you should put the book in locker or you could try write on the paper about lists of books and stick in the place where you can see. Tell your friends should remind you on facebook, line or call. Maybe you should check your bag before going to school. Last, when you forgetting to bring your books that you should borrow your friends