Classes in Classroom & Schoolwork will mirror what is in Apple School Manager, or Jamf Pro if "Enable Apple Education Support" is checked. If you also have "Enable Apple School Manager Integration" checked, users and classes will be synced from Apple School Manager to Jamf Pro. It sounds like you may have multiple entries from multiple data sources causing confusion. You have a few options...
1. Clean up the data in PowerSchool. If the data in your SIS is not being maintained, it's probably best to not import that bad data. If the data in PowerSchool IS accurate, but not syncing with Apple School Manager, contact AppleCare and/or PowerSchool.
2. Switch the Directory Sync option in Apple School Manager from SIS to either Google or Azure (depending on which you are using for Federated Authentication). This will bring users over from your IdP, but no roster data. You will need to manually change the role for teachers from "Student" to "Instructor," but then teachers can manually create classes and add students in either Classroom or Schoolwork. Classes can also be created manually in the Apple School Manager web UI.
3. Alternatively, you could switch to IdP Directory Sync for users, and sync those users with Jamf Pro, and manually create classes in Jamf Pro.
If the data in your SIS is maintained and accurate, resolving the sync issue is probably your best bet as it should minimize the work for you and your teachers.
