I'm not sure where 27th May has come from - the general consensus among schools is that after your last exam, you're more or less finished, unless they're carrying on with some teaching (that seems pointless to me, but there are some schools doing it). The last date for teachers to submit your grades to exam boards is 18th June, and according to my head of sixth form the official legal end date is something like the 9th July (that may not be exactly right, it's sometime around that date). By that, he means we're legally enrolled at the school until that date, but we're on 'study leave' (he has to call it that so that we don't have to come in, but technically exams at my school finish this week). Again, it'll vary according to school, so I'd email one of your teachers and double-check what you actually have to come in for.