Hm. This I do know a little bit about. Education definitely wasn't free, and in pretty much every pre-industrial society most people don't really have one - even if you can afford the fee, it's too expensive to not have the children working. There are certainly plenty of legal documents and the like surviving that begin with one name and end with somebody else's signature, with a note that the second person signed it on behalf of the first, who was illiterate. On the other hand, there are a couple of cases like the poet Horace, who grew up a relatively poor farmer's son, was sent to Rome for an education and ended up mixing with the very top of society. That might be a little bit of a self-made-man myth, but we do know that you had to be literate in order to be a centurion, which means that at least a couple of percentage points (allowing for a few premature departures from service, and the desire not to promote the totally incompetent) of the lower social ranks could read and write, even if that came through a rather basic barrack-room education. There's also a surprising amount of handwriting - whether scratched into the walls of Pompeii, on religious dedications or 'curse tablets', or on wax tablets, which have been found at Hadrian's Wall and recently in London. Now, this isn't all particularly good Latin, and it's the sort of thing that's used as a source for spoken Latin, on the grounds that their 'mistakes' probably reflected how they thought the written language 'ought' to look. Nor should we assume that the ability to scratch 'Marcus had sex here' into a tavern wall implied the ability to read the Aeneid. But there's certainly more reading and writing being done than you might think.