If you feel, you can read on your own, without attending classes, it simply means, you can still relate, or you've once had the idea of what you are reading, it simply means, this is not your first time of reading such topic. If not, it is wise of you to go to class, attend lectures, make a note, follow your lecturers laid down steps, watch them close, listen attentively, and if you do otherwise you will be reading the unnecessary, and if eventually you don't fail, you will always be a mediocre, an average student!