training worker stats

[Keme]

How do we train a worker in stats like endurance? Do you have to have a building with a school, or can only city workers gain form schools? My dowser and hunter don't seem to be gaining in their stats on the trail, and my dowser (who I put in the city because she had the worse endurance and I wasn't able to let them ride for part of the journey) isn't gaining anything from staying housed in a insulae. I'm currently raising my cities school prematurely, just in case. I hate wasting money and time unless it is really needed.