Do my teachers need accounts of their own?

Yes, and that is the good part — invite them from the Teachers menu, and each one signs in with a mobile number plus a PIN on their own phone. They only see their schedule and their own classes' attendance; invoices, amounts, and students from other classes stay closed.

Attendance is filled in by the teacher from a phone in the classroom, and the moment it is saved it has already deducted the students' packs and is readable by parents. Nobody has to copy a paper register over at the weekend.