I don't know details regarding security of school buses, so I can't answer OP's question.
There are no details at all, because, as has been confirmed by all three people who have posted here who know what an American means when he/she says "school bus", there are virtually no school buses in Poland.
I know that there definitely are school buses in Poland and you posted nonsense misleading to the OP,
Really? Perhaps you can post some links or some pictures? Didn't think so.
the school bus in my ex village was a regular bus, but running to a timetable that accommodated pupils. the head master/teacher also rode the same bus, as did one or two teachers. the service didn't run during school holidays.
Same here (but it was a town of 14,000 people and the biggest civilisation for 50km in any direction).