Things have changed a bit since I was at school. I did work quite hard during my lower sixth year and was actually able to take my foot off the gas a bit in my upper sixth, but most people coasted through the lower sixth and enjoyed life, and maybe did an extra GCSE on the side, and still got decent grades at the end.
Now the pressure seems to be on all the time. I'd have thought a lot of people do badly in exams because they haven't put the work in, not because they don't have the ability.