With Zearn, student data is maintained within student accounts; this allows students to retain their progress and badges from year to year. It is not possible to delete student badges without deleting the student's account.
While teachers cannot delete lesson badges, they can reset their students' assignment to the beginning of the Grade, Mission, or Topic. Once the assignment has been updated, the student will work through their Next Up feed in order from the assigned point. All badges earned by the student previously for the assigned mission will be visible, but the student will not be able access future missions through their My Stuff feed until they complete assigned lessons again through their Next Up feed.