Literacy rates?
I'd say (guess?) nobles and clergy are always over 90% literate after 1400 AD.
Now by the 16th to 17th century we see a percentage of nobles existing at:
England/Britain - 2% noble population
Spain - 8% noble population
France 3-5% population is nobility
Poland-Lithuania 10% of population is nobility
Italy - 1-5% of population is nobility (Depends where in Italy)
However not all trends remain the same. Poland, Spain and France all had for example impoverished nobles, for various reasons - such would be unheard of in say, southern Germany. France had special charity schools opened to educate ladies of poor and impoverished noble families, for example. In Poland-Lithuania we find cases of nobles starving to death in wartime famines because they simply cannot afford food. However in Britain (England moreso than Scotland) we find nobles controlling massive amounts of lands - thousands of acres for many estates for a single noble and his family, as compared to the 5 acres given to normal serfs in that same land. Generally the trend is, the more nobles, the less power shared between them - however does this play into education? Money always does
Does anyone know clergy population estimates around this era? Add it to the noble population, and you have your it - until the rise of the middle class (Again this screws up Italy's statistics earlier than most nations)
As for ancient nations, I simply have no idea.