Ive only had one successful grad from my GG school.
Kurumster aka Steve aka best MI in your world.
After teaching many people GG or other related games for years, I realized something. Don't teach people who cant take criticism, and who don't understand how to learn on there own. I had a bad habit of babying new players for anything, just hoping they will get better. With kurumster it took 1 week, heck thanks to him I learned more match ups and was able to play the game more which revitalized my interest in the game.
How I see it, if they don't improve in any aspect every week, drop them like a doren combo.