I knew an elderly - nearly 100 at the time - man many years ago, when I was only a child, who had been what they called a "Half timer" - half time at mill, half time in School, when he was young. He wrote a beautiful copperplate signature, and was justly proud of it, but really could hardly functionally write, and his far younger wife confided to my parents that he could scarcely read. But his signature on his first wedding certificate would have been impeccable!
We hard a lot about poor literacy levels today - and there are always wonderful copybooks in museums.
But bearing that old gentleman in mind, I wonder how many others there were of similar attainment. Sunday Schools did marvellous things, before board schools were established, and were the first line of learning for many, but you had to go there in order to learn, and many honestly felt they did not need to. Most schools cost pennies each week - but pennies were not easily come by, for many.
Many more were probably functionally illiterate than we assume. I know that in the 1950s it was not that every child left school able to read and write, it was often that some did not ever attend school, because of assorted handicaps, whereas today, each child is accommodated somehow, to some level, in the system.