Assign a Substitute Teacher

A substitute covers one occurrence — the reservation and every other week keep the regular teacher. It’s set from the weekly calendar’s lesson modal (the “Substitute teacher” select), or implicitly by dragging the lesson onto another teacher’s column.

Who can be picked

Anyone on staff — the select lists every teacher in the system, not just this semester’s roster, because cover often comes from someone who isn’t teaching a regular slot. It’s grouped into “Teaching this semester” (labeled with their locations) and “Other teachers.” The first option, “No substitute — the usual teacher,” clears the assignment.

The one hard requirement: the substitute has to be free at that hour. The pick is conflict-checked against the substitute’s own lessons and hold blocks at that moment, and an already-booked cover is refused. (There is no check that the substitute is assigned to that location or semester — that’s deliberate; clearing a substitute needs no checks at all.)

Location is intentionally a separate dropdown in the same modal: picking a cover teacher who is based at the other building must not silently move the family across the borough. If the venue really changes too, set the location override explicitly.

What changes

The write is one field — lessons.substitute_teacher_user_id — but the “effective teacher” of a lesson is computed as substitute, else the reservation’s teacher everywhere in the system, so:

• The lesson leaves the regular teacher’s day and appears in the substitute’s day view and Teaching Days — even if the substitute has no regular column that semester, the calendar grows one for them.
• The substitute can mark attendance and add notes; they count as the lesson’s teacher for access checks.
• The substitute’s time is now blocked at that hour for every future conflict check.
• On the admin weekly calendar the cell is tinted pastel orange with a “Substitute teacher: Grace Lin” note; parents and students see the same note with the substitute’s name on their schedule.

Undo it by selecting “No substitute” (or dragging the lesson back onto its own teacher’s column).