One password for the whole school, written on a classroom board.
Every student and staff member signs in as themselves.
Students pass it to friends, and the neighbours have it too. You can't tell who's on, or switch one person off.
With their number and a 6-digit PIN. PINs go by SMS or email, or on printed slips for students without a phone of their own, and always for secondary pupils. A lost phone can be stopped from the helpdesk.