I have a few companions with the trainer skill, including my own character, and it seems like the skill is only working with other companions. Regular troops are not receiving any experience at all from it. We are all around lvl 6 so I doubt the issue is that troops are higher level than us since not even farmers get experience.
Is trainer not supposed to give experience to troops for some unknown reason or is this a glitch?
Did you check the level of the troops you are trying to train?
Training skill works, but there are things which lessen its effectiveness.
You need to be higher in level than the troops you are training.
If you have 30 farmers in your group then more of them will be ready to upgrade after midnight than if you only have two in your group. They pool experience and 30 farmers will get enough experience for a handful to upgrade. If you are only level 6 then you probably don't have a lot of points in training skill and it's not giving a lot of experience for those few higher levels that you have.
To be frank, if I were you I'd not worry about training skill until you are level 20 or greater. Here's why:
1. You don't have the money to pay for upgrades. You are still equipping yourself and your companions so trying to build an army will make you go broke.
2. You can recruit more troops faster from captured prisoners.
3. You will need to get more levels before you can even afford to put points in a party skill like that, but also, the points you put in won't be effective at low levels.
You'll be better off babying peasants until they level on their own than trying to level them with training skill. But even then you're still better off recruiting from captured prisoners.
Why train up peasants when you can have some Robber Knights? Yes, their wages are ridiculous but you can always disband them before payday and then recruit some more. Just sayin'.