Capacity is physical. Twelve benches means twelve students, so a waiting list that automatically offers a cancelled place is worth more here than any advertising — the place is gone the moment the term starts.
Materials are the invisible cost. Clay, glazes, paper and paint consumed per course, measured rather than guessed, is what tells a school whether the pottery class actually pays.
The kiln is a shared resource with a queue. Firing schedules, whose work is in which load and when it comes out is the detail that decides whether the last week of term is calm or chaotic.
Workshops and terms need different handling. A one-day session is bought as a gift, paid up front and often transferred to somebody else; a term is a commitment with instalments and attendance.