Why does a student appear among a class's regulars?

A student is a regular of a class in one of two cases: they belong to a group of the session, or they came (present or late) to at least 2 of the last 6 held sessions of this class (default threshold).

A "held" session is a non-cancelled session whose attendance was taken. The owner sets this threshold in Settings > School > Regulars (at least 1 to 20 visits in the last 1 to 50 sessions). In a school without groups, regulars only appear after 2 or 3 weeks of attendance.

The owner can remove the student from the group from their profile (Edit, Groups), but that does not take them out of the regulars if they still meet the threshold: they leave when their recent attendance falls below that threshold. Other active students are under "Other students", sorted by recent attendance at this class.