How do you see yourself entering this data?
Do you go to the record of a student and do you then select the activity (or activities) this student is in?
Or do you go to the record of the activity (Hockey) and do you then start adding students?
Maybe you could select the class first and then see only the studens that are in that class.
I'm thinking maybe you could use a join table. That's probably most flexible.
But if you want to keep it simple you might use checkbox sets.
But that might be less flexible.
I suggest you modify the design of your database.
Instead of using multiple fields to list the classes that a student is taking, you create records in a related table that list the classes in which they are enrolled and then another related table lists the activities that they enroll in. I am assuming here that a student can enroll in multiple activities from a single class.
The exact structure depends on how you need to manage enrollment. (A high school may neede different tables, relationships than does an elementary school...)
A "class" might be "Mr. Smith's 3rd grade class". Or it could be 1st Period Algebra I Taught by Mr. Smith. (and a 2nd 1st period Algebra I class might be taught by another teacher...)
basic set up for enrollment is:
But if you need to track enrollment by subject, teacher and not just by "class", you may need:
In each of these diagrams, ---< stands for a "one to many" relationship.
With either approach, you can record/track enrollment in activities by class/session enrollment by using these relationships:
If you haven't used portals before, you'll want to look them up in Filemaker help to get more info on them as they are most likely what you will be using to work with these tables of related records.