My initial thought is that you'll want one table for students, one table for events, and a join table that will sit between the two. The join table will essentially allow you to have a many to many relationship between students and events. Every time you create a new event record, you will probably want FileMaker to import all your students into your join table. Each of those newly imported records will not only point back to one student record (each), but they will all also point back to the newly created event. This way, they can all be seen in a portal from the event, and you can toggle their attendance accordingly.
There are a number of threads that discuss taking attendance here in this forum. You may be able to find some of them with a bit of searching for the keyword "attendance".
In addition to Matthew's suggestion, many folks find that they need two sets of relationships, one to show who is enrolled in a given class or class session and one set to track actual attendance. Some times a script that runs through the enrollment roster generating one related record for each student for the next class meeting is helpful.