Having been in situations where student mobility is a concern, I was frustrated by new students entering after I had everyone else settled and supplied with class information. This year, when making your "Welcome Back" letter, do not date the letter and simply title it "Welcome to Room...." Include homework info, special class days, a supply list, and an invitation to meet with parents to answer concerns. These may be given to the class during opening week, but be sure to have extra copies. When a new student comes to your class, simply send home the "Welcome" letter...and the letter will be usable in November, March or whenever!