[makomk]

Not closing schools was the government's preferred option for exactly the reason you point out. Unfortunately, the teachers' unions had different views on the matter and it's rather difficult to keep schools open without teachers, especially when they can easily just carry out a mass sick-out. Exam halls are probably a bit of a transmission risk though since they involve a bunch of people who wouldn't normally mix sitting in the same room sharing the same air for a few hours.

[nicky0]

Also once the schools have been closed it becomes a lot harder to properly prepare the pupils for the exams.

[smcl]

You’re right and this is often ignored - the few weeks or so prior to exams where the curriculum is largely over can significantly change your grades