Within 24 hours
After an import, the Learners page carries a note: 38 learners were imported 20 minutes ago. You can undo that as one action until 4:15 PM, 8 June.
- Press Undo import in that note.
- Read the confirmation — Undo the import of 38 learners? Their scores, if any, are kept but hidden with them.
- Press Undo import again to confirm.
What it takes back
Only the learners that came in on that import, and only those. Anyone you added by hand before or after stays. The learners are taken off every subject in the class as well as off the class list, so no subject is left holding a name the roster no longer has.
Nothing is destroyed. Removed learners and any scores against them are hidden, not deleted; the retention purge is the only thing that deletes for good.
An import done in the class setup wizard counts as an import too, and is undone the same way from the Learners page of the new class.
After the undo
Correct your sheet and paste it again. The undone learners are no longer on the roster, so they will not be flagged as already there.
After the window closes
Once 24 hours have passed the note disappears. If you press an undo link that has expired, you get: That import can no longer be undone — the 24-hour window has passed. Remove learners one by one from the roster instead.
Removing one by one is Learners → Edit → Remove from roster on each row. For a learner who was really in the section and has left, use Mark transferred out instead — that keeps them on the class record with their scores intact.