In this fantastical medieval world, knowledge is a precious wealth.
Not to mention slaves, even commoners usually have no chance to touch this kind of wealth.
As for the nobles, of course, they don't need to worry about this. Their castles are filled with books, and they even have private tutors in charge of their education.
But for commoners, it's hard for them to learn.
They mainly have two ways to master knowledge.
The first way is through the Church.
The Church has schools in various places for commoners to study, but here, children mainly learn theological knowledge. Besides being instilled with how and why they should serve the deity, they hardly learn any useful knowledge for daily life.
The second approach is through the nobles.
That's right, nobles also recruit some commoner children to accompany their children in their studies.