Classroom management! Input students, remove them, input grades for everyone, calculate averages and scores. As a bonus, read and write to file! There are lots of things you can do with this, not to mention being practical. OK maybe not to YOU but this is a solid base for managing large amounts of info. Make sure to make the Student class and the Assignment class. More if you want, but not less.
It may seem hard but it really isn't. But it defintly is tedious! Be careful, not to trip your self up because this is going to be a long program. Good variable names, function names, orgranziation, and notes will get your through this! Work smart, not hard! There are alot of ways to get this done fast, but I'll leave it to you to figure them out (;
If you don't know how to work with vectors / lists then I would suggest you start with a limit of 10 students and 10 assignments.
Add file input and output support. Ask to write all class info to a file. And then ask to read it in again when you open it up. Next stop, databases!