Actually, the British officers of 1917 were mostly middle and upper middle class folks and not the aristocrats of three years earlier. The latter had pretty much ceased to exist between the fighting retreat of 1914 and the disasterous Somme offensive of 1916.
Who tended to have a pretty decent education by today's measures. (My favourite of the poets was from an upper-class, although not ennobled, family: Siegfried Sassoon. They of course were never ennobled because they were not C of E. Siegfried spent much of 1917 in Craiglockhart nuthouse).
English schools were pretty decent until the 1960s and 1970s, when a campaign of levelling eliminated the separate tracks for knowledge workers (Grammar Schools) and labourers (Secondary Moderns), and consolidated all secondary education at the lower level (Secondary Comprehensives). It created a business opportunity for a lot of new private schools, though.
I've encountered many graduates (and even dropouts) of the grammar schools that have a cultural knowledge level higher than today's college graduates.
d.o.l.
Criminal Number 18F