Problem re- establishing a relationship

Somebody did some editing on the Access Database over the summer and messed up the relationships I had in it.  I had to create a new table (columns ClassnumberN (key), Classnumber, ClassPrefix).  I have a numbered field (ClassNum) in a table called Appointments that I use to reference this table so we can keep track of which class a student is seeing my office for help in.  My problem is now with the relationships.  I created a one to many relationship between the two tables, but if I select a class for one student, it changes the classes for all of the students in the database.  I am fairly sure this is a referential problem, but this was not how it was working when I left for the summer.  
I am having trouble finding the issue.  Any help would be appreciated.  (I am trying to avoid recreating the entire database and importing the data.