Classwork in Japan as an exchange student?

Hello! I want to go to Japan as an exchange student, but there's just one question bugging me.

This goes to anyone who has been to Japan as exchange student – or maybe to those who haven't, but know the answer to this question. What is classwork like in Japan as an exchange student? Will I have to do the same as everybody else, or can I do my own classwork from my home country? And if I have to do the same as everyone else, will that disrupt my studies back in my own school?

Those are the main questions I can think of as of right now. Thanks in advance.