Comparing it now with when you first saw it
I first saw this when it came out in 1982. I was 11 and in my last year of primary school. I looked and acted very much like Alan and could recognise a lot of what he was going through; the crush on a pretty girl in class; the use of prayer as a cosmic request service; the long summer afternoons and games of cricket; the ropey school play and the goings on between the staff that were only dimly understood. I can still remember the butterflies in the stomach sensation when he leaned in to kiss her and the torment when he couldn't go through with it.
Looking back now as a 37 year old, I don't have those pre-adolescent feelings anymore but I do appreciate a lot that I didn't notice as a child - the comedy in the Alison Steadman/Groundsman relationship completely went over my head but now I think it is hilarious. Also the way that by the end of the film Alan has unconsciously hit on the manipulation of female psychology that any seducer will recognise - the girl likes him all the more because he decides he doesn't like her any more.
Also, this is one of the best films for period detail. I wasn't around in 1948 but it all looks completely correct, the clothes, hair, cars, speech, mannerisms etc.