Heroes 5.5 WarGame Edition - Tactical Edition.

Retraining works ONLY for knights (it doesn't work for paladins or temple guards). Unfortunately, this limitation cannot be fixed. That is, if a knight doesn't appear in the tavern during the game, you have to play without retraining (fortunately, the racial unit itself will be strengthened up to double the stats or so).

I heard about this myself, but I haven't seen it. But the fact that this perk was removed in the multiplayer tournament mode (RTA) is already an indicator that the flaws in this perk are too severe to leave them in.
I will try this perk sometime, but for now, I consider it dead by default.

It has been fixed differently:
1) Orcs no longer have education at all.
2) There will probably be no mentor on the maps.
3) Natural stats for education will not be given (by editing the executable), instead, exactly 2 stats will be given for each skill level via scripts, this will fix the imbalance of the skill in long games.

Actually, why does an orc need education if the perks in it should be magical, and orcs don't have magic? Just for the stats? That's not a reason.
An orc is a smart warrior. An orc will not study. An orc will fight.