Your fighter starts of with 1.95, every - is a step of 2.5
So
<2.5 --
>2.5 but less than 5 -
>5 but less than 7.5 +
> 7.5 ++
Now keep in mind they start with 1.95 and the value is not calculated 5 + 1.95 but the total value in self, so if he has 5 it is with the 1.95 (actual learning speed would have been 3,05, but that is not how we check speed).
So in short, he needs top go from -- to + in 1 session to be decent or better. If he only goes to - then that means he is slow but to know exact how slow you need to use grease monkey script.
He could be 4.95 and sacking some one for that when all other stats are good is personal preferences.
Having said that tho, I've had my share fair of slow learners and they are rarely worth it, they need to be decent else it's 2-3 years (IRL) before they are really competative