My theory is they simply can't run these 'cram sessions' others are talking about because they are so short staffed. So many classes are cover already, and there's no staffing headroom or classroom space to take students or teachers off timetable.
That could easily apply to DS school.
I think one of the reason they finally decided after half term there is study leave is because it will free up teachers and that they can drop some of the supply.
It's not so bad today for DS all the lessons still have exams so they'll be doing revision hopefully and tomorrow an exam - which just leaves Friday. He says it's quieter as well so suspect many aren't coming in on none exam days anyway or disappearing after the exam.