Two points I'd like to make. The first is about ability, since it's been raised again on this thread, a favourite subject of mine (Cortina dusts down her soapbox) :):
I believe that intelligence is learnable (to a degree) and that ability does not have a ceiling. I used to think like Le Queen and it held me back for half a lifetime. I am no mathematician so a good grade at GCSE or A'level is 'impossible', I am no athlete so the London Marathon could never be achieved. Now I see that with lots of work from me, and a good coach/teacher and the right environment, both are within my grasp. There's a whole raft of research out there to back this up: Prof Lauren Resnick at the Uni of Pittsburgh, Harvard's Prof David Perkins, Carol Dweck, Guy and Bill Claxton etc.
Back in ancient times, in 1938, we saw things differently. The Spens report was used to implement the Grammar and Secondary Modern 'divide':
Intellectual development appears to progress as if it were governed by a single central factor, usually known as 'general intelligence'..It's possible at a very early age to predict with accuracy the ultimate level of a child's intellectual powers'
I wish all our teachers believed in the concept of learnable intelligence. Reason being that their belief systems will entertain the possibility that most of their students are capable of doing very well in the classroom and outside. You have to discard the belief in fixed IQ and ability ceilings if you want people to be interested in learning how to learn. Effort is then a pleasurable stretch if it means you can and will get better with practice.
I am not saying there are not genetic differences in IQ, but the most important thing is that everyone has a wide envelope of variation around that 'base point' that depends on experience, encouragement and self-belief.
Intelligence isn't unitary it is the sum of all of your habits of mind. The habits of mind are many and various and most of them can be cultivated.
My second point is about whether the exams have got easier etc debate. My point is that now we seem to value different things as a society. We value the practical over the high brow, we no longer value 'knowledge for the sake of it' etc.
O'levels used to be either a pass or a fail. My Dad's 1956 English paper asked for various words to be put into a sentence to illustrate their meaning. I remember one was the word 'loquacious' which I as a 16 year old would have had no idea about (I believe the majority of adults today would have no idea either). Things have changed some would say this means things have 'dumbed' down, it depends what you value.