Harpers taught people how to read, but unfortunately it was considered an unimportant skill when most people worked everyday and had little need to read anything. So maybe they got the basics when they were young if the hold was lucky enough to be on a Harpers route. The larger the hold, the more likely it was they had a Harper. Weyrs usually had one, sometimes a dragon rider with Harper training (weyr singer) or they had one that made the trip regularly from the major hold they bound to.