Education was very different in the 1920/30s and even the 40s.
There was a lot of learning by rote and the three Rs. Not a lot else. No investigation type learning, no exploring literature.
There are other factors at play as well.
Unions offered education, the Quaker chocolate makers offered education.
In may places, in the 1930s libraries were full of unemployed people just keeping warm. But while keeping warm would pick up a book.
People generally learn the skills they need for life, things like meal planning were essential in the war.
Until the late 1980s it was quite normal to leave school without qualifications.
I sometime struggle to explain things to do with education to my mother because she has no experience of university learning. To her an essay is something you are given a title for and told to write in one evening and hand in the next day, not something you take a number of book out of the library and reference.
One of my grandparents went into a primary school (many years ago, she has been deaf for years) as a 'guest speaker' to talk to primary children about school and for them to ask questions about what school was like in her day. That is the kind of experience that was not available in her day, for 6 year olds who have been doing history or their town it was like asking an historical figure.
A couple of people have mentioned the children who did not go to school or who were 'sent away' and forgotten about. That did happen.
My other grandmother had a cousin who was described at the time as 'simple', now I think we would say she had a mild learnig disability. She did go to school with my grandmother, but she never left what would now be reception class.
Strangely enough she did learn things after she left school. When her (grandmother's cousin) died her sister used to draw a picture of the clock before she went to soerk and say "when the clock looks like this put the dinner on and I'll be home when the clock looks like this"
Within a few weeks she had learned to tell the time. She then went out and got herself a job as a cleaner.
She left school illiterate and inumerate. I don't think that would have happened these days.