I have only built the Academy in my several games. I never had the time/resources/priority to build higher-level education centers. I also only build one in my capital.

Here is what I found out. Every turn you have a faction member in the town, a random chance occurs (decent chance) for a new retinue member to join up. I have had several join one leader and also spread over the leaders in a town in the same turn. For the Academy, it seems to be (from memory) librarian, mathematician, the doctor guy, the public health guy (also sort of acts like a doctor buy troops have negative morale if his is present), and biographer. I might have missed some. Most these add to management and/or influence.

Since you can move the retinue members from leader to leader, I usually strip my governor of any that show up and move them to other leaders. New faction members usually stay in town for several turns to increase the chance of free retinue, including a priest from the temple. I eventually get a worthless faction member whose job is to move retinue from one leader to another. I do stuff like have two governors move half way between their cities to link up, transfer retinue, and move back home in the same turn.

I also strip retinue from anyone 60 years old if I can. Especially the ones that make units cheaper to buy. Those retinue guys get piled onto the governors of my main recruiting cities.