I agree with RTN11 reply I would just add that on issue of new rating a class 1/2 medical needs to be valid but as a renewal no you dont have to have a medical to fly under tuition ,only to exercise the rights of "your licence priviledges" in other words to fly on your licence which you would not be doing.The pilot in command is the instructor. A flying club on other hand may have insurance issues (requesting all licence holders to hold valid medicals ect.)so you would also have to check with them about that.