For the vast majority of my ancestors, when going back in time the sociocultural level gradually decreases until I end up having poor farmers. The rate at which the level decreases depends on the branch, but this pattern is globally universal.
I'd like to know how can I estimate which of my ancestors were literate and which weren't. I guess this would mean to know when various countries introduced obligatory school, even for the lower and less privileged classes. The countries I'm interested in are: Switzerland, France, Germany, Austria.
The earliest ancestor I'm 100% sure was literate and poor farmer, because I have a letter he wrote, was born in the 1820s in Switzerland. His handwriting is good but his orthography is absolutely awful.