@toothbrush
Seems legit to me... Imagine, if you would, the kind of crazy Karens about with their "precious little angels". Now imagine that they have a not insignificant amount of political power. If you raise some kid up a grade from another noble they see that as basically saying their kid isn't as good as this kid.
Saying about pride is being diplomatic, the reality is he doesnt want to deal with Crazy Noble Karen (hereafter referred to as CNK) screaming that if he doesn't raise HER kid up a grade she'll ruin his damn career.
The CNK will still say it's the schools fault if her thick kid ends up looking even thicker in lessons they're not prepared for. so for everyones sake it's best that it's not even an option.