From Longman Dictionary of Contemporary Englishstay after (school)stay after (school)SESPUNISHto remain at school after the day’s classes are finished, often as a punishment → stay
Examples from the Corpus
stay after (school)• I had a friend who worked for the oil people, and I decided to stay after a visit to this place.• But Lucie stayed after all, to play Balaam, and Izzie to play her pipe beforehand.• Some stay after class and follow me devotedly around the campus.• I stayed after hours doing murals on tailgates.• Keegan is desperate to stay after savouring his first taste in management by keeping United in the Second Division.• She went so far as to make special transportation arrangements for some students to stay after school to finish their assignments.• In May, when the time changes and the weather mellows, the team will stay after the games to picnic.• I have never once heard a staff member say that wouldn't stay after the school day for some activity or other. 