I tried your link but the system said 'download prohibited by the uploader' (or something similar) so I can't see the file you shared. I think you need to modify the upload.
Make sure to base your report layout for this on the join table. You can perform a find for the relevant records and the relationships in place can then be used to pull in data from Students and Class.
Right, that link works but the file has security on it so I can't open it.