Solved

Training question

Why is one of my driver's getting 10xp per training session and the other driver getting only 3xp per training session?

As long as drivers level is (way) below your managers level, he trains pretty well. When your driver is above, he always gets only 3% each session.

Btw, do u think this is a fairly often asked question?
http://letmegooglethat.com/?q=igp+driver+training+3%25

Indeed it is. 

Thank you.