I can't find the documentation on the trainer career (it is from the careers modul, right?).
I have a Sims who I am sending to the ballet studio with Arsils generic role. She is athletic and a trainer and I thought she would use the ballet bars and train herself and other Sims. Instead she is reading books.

Hi There... the Trainer Career is in the Self Employed module of Careers. Not sure how much help this is but are you directing your sim to train on the bars or expecting him/her to automatically train? I've never tried training on the ballet bars but for some types of trainers they have to have attained a certain level to be able to do so.

She does have the ability to train Sims when user directed. I just thought she would try to train Sims on her own, but apparently I was wrong.

This doesn't push Sims to train, it just pays them for doing it.

ah alright, is there anything that increases the chance of a sim training another? certain traits? high logic score?

Changed the lot type to gym (which i had not before because i did not want all sims to do ballet) and locked the doors to only let people with appropriate traits through. Now she behaves like i expected.