Sometimes Will Schuester thinks he is a horrible teacher. He sees these kids come in every week with new problems, and old unsolved problems, and even a few ancient wounds, and he doesn't know how to heal them. And when he tries, he doesn't always get it right. He knows his decision to not give Rachel and Finn their traditional solos was right. All the kids deserve to a chance to shine. Maybe he shouldn't have yelled at Rachel: but he can't bring himself to regret that very much. The girl needs an attitude adjustment, and badly; yelling at her probably won't help in the long run, but it got them all out on that stage, which is what he, and they, needed in the short term.
And when he thought back to the duet competition, he thinks he understands a little of Rachel's bitterness at Quinn and Sam. Although he hadn't thought much of it at the time, the only names that hadn't shown up in the voting were Rachel and Finn. Those two were the only ones who hadn't voted for themselves, and they had done it knowing it ruined their chance to win. To be frank, he's still a little incredulous about it, sometimes feeling that there must be some other explanation for it – insanity, coercion, anything. But, he supposes that if he had tried something relatively altruistic and it had come back to bite him in the ass, he would be inclined to lash out as well. That didn't change the fact that generosity and teamwork were still qualities that Rachel needed to work on.
He wonders though, in his rush, if shining the spotlight on football players and cheerleaders maybe missed the point about opportunities to shine. Looking past Mercedes and Artie and Tina was a cruel extension of the way the school also seemed to treat them: as if they didn't exist. But he likes that he gave Santana a solo, even though sometimes he feels bad about what seems like a reward for her cruelty. But maybe -maybe- if Santana can learn to feel good about her own accomplishments, she won't need the casual sex and the bullying.
His worst dilemma now is trying to solve Rachel and Santana's rivalry. Watching two girls lash out at each other, when he can see who they really hate is themselves, is maddening, especially when it was over boys who -although they never meant to do it- were close to the core of each girl's self-loathing. But he knows that he can't fix this. He would love to sit them down and open their eyes, make them see the sheer insanity of what they were doing, how much better they could both be if they wouldn't tear each other down. But he can't. It's not really even his own failing – what man, what teacher could do these things? It's something that the girls will have to discover for themselves. He just hopes it happens before they destroy each other.
Will Schuester knows he isn't a terrible teacher. But that doesn't mean he doesn't feel like it sometimes.
A/N: Ok, my point here is basically that Will doesn't always do the best job, but, honestly, these characters have enormous problems, and he can't be expected to be right all the time. Also that both Rachel and Santana's crazy is sort of sad and sympathetic.