Article here about the great grammar schools of the 50s
"In 1959, grammar school pupils represented the brightest fifth of their age group, yet nearly 40 per cent failed to pass more than three O-levels. Complacency seems to have been endemic. In one Dorset grammar inspected by HMI in 1956, a third of pupils left with no O-levels, yet the report concluded that this school, which took only the brightest 17 per cent, was ?good?."
"A 1950s Ministry of Education study found that fewer than 0.3 per cent of pupils leaving with two A-levels were from the unskilled working class. Even among the top grammar school streams, a third from the poorest backgrounds left without an O-level. Many poorer children left even before taking public examinations.
Even before the 1944 Act, a child at grammar school was often a sign of an already upwardly mobile working-class family. Rhodes Boyson, a minister under Margaret Thatcher, was portrayed as the archetypal poor boy who succeeded solely as a result of his grammar school education. But what was cause and what effect? His father was a full-time union official and councillor who, unusually, owned his house before the war. He was even chairman of governors at Rhodes? school."
Interesting reading.