Round here hardly any schools have real exam leave.
I think the logic is that most students are unlikely to do much work at home.
They stay in school full-time until all the core exams are over. If a particular subject has finished (exams all over), then they continue to attend and are supervised by that teacher, but can revise other subjects.
I think it's a good idea: ds1 is still 15 and doesn't have the maturity and motivation to do hours and hours of independent revision unsupervised at home.
Apparently ds1's HT is keen to send students home on exam leave earlier rather than later. The Heads of Dept are objecting: some are still teaching the curriculum material. I hope she gets over-ruled.
If your school does have exam leave:
a) When does it start?
b) What sort of school? (state, independent, selective, etc)