Considering he’s having major problems getting his own spells to work, having him teach would be ineffective at best and disastrous at worst. He’d be better off teaching something he actually knows, because then he’s not a half-bad teacher. He’d outright refuse if asked, because what in Oblivion are you thinking I can’t teach something I can barely do myself???
If forced, he’d just not show up, consequences be damned. No way is he going to stand up in front of people he doesn’t know and tell them he’s stupid unfit to teach the material.