I think AS exams are possibly the hardest because they have only been doing the course for 8 months.
GCSE's are studied for at least two years, sometimes three. A levels build on AS knowledge, experience and practice and they start the courses this summer before they break up.
Many students this year went into completely new environments and/or had completely new subjects and a whole lot of new people/teachers to get along with.
Of all the years in education, I think this is the most demanding (with the possible exception of first year at university which holds similar challenges).
So well done to all of them. There are many options going forward and nothing is set in stone. I think they've coped brilliantly and I hope you all have a fantastic summer and a good, long rest 
(But let's get the rest of the exams over first
)