In terms of evidence - if you google it you will find a lot sources which indicate a far higher level of literacy from that period - just as studies show that 50 and 60 year olds (the next gen on) have higher levels of literacy than the current generation - Gove sought to try to reverse that to be fair (I am not a Conservative!) - literacy levels and education standards have dropped and dropped
But at the same time, yes it was higher overall but there were groups who were written off too, as I understand it. Was your dad in the lower stream, just out of interest? It wouldn't shock me if it had been as he said, I am really interested to know more. What was the difference in terms of teaching in relation to the top, middle streams?
I am not sure what you mean in relation to leaving age - there were higher standards across the board whether they left school at 15 or not? Sorry, just not catching why that is relevant as i talked about 40 percent failing at primary, and at 16 (which is only one year after 15)
Teaching methods - they were extremely strict and not creative, as I understand it. The progressives in the 60s wanted to cut out strict and only include creative. So in the 70s and 80s you saw primary schools totally cut any academic work and only concentrate on drama, art, etc. Which was disastrous and absolutely awful for most of the kids. Whereas it would be better for children to split the day, having part of the day strict and part of the day truly creative ie allowing self expression.
What they did do better was in terms of expectation and curriculum, and resources - I have grammar books from the 50s aimed at primary school children and they are amazing - more comprehensive, more interesting, more demanding, all useful
The fact that it was strict also needs careful thought. It was shaming and sometimes physical and unhealthy according to most sources, which we now consider to be so damaging it actually knocks out the benefit of literacy and maths competence. Strict is important but motivation and personal attention works a lot better than force and shaming. So that side of things was not good.
We know a lot now via research about how children's behaviour should be managed, to bring up happy but also responsible and aware children - this isn't being done in schools and there is no reason for it. We still see to much shaming. We know punishment doesn't work yet in senior school constant petty punishments are used - which stress kids out so much it affects their ability to learn.
I would be really interested to know more about what your dad said about his education at primary and then senior.