I think his strictness is partly his own personality but also a desire to help students like Touko. It's not that he wants them to different from her in the sense that he thought she was bad, but more like I think he wants to make sure they stay on a successful course so that they can be whatever they want to be without worry. With Touko, though she herself was a nice person, she had to have the determination and help to get her grades up in order to have a chance at achieving her dream. Likewise, I think he hopes that if he gets these kids to take things seriously now, then they'll be in a position to choose what they do rather than being stuck with what's left.
Is he the ideal teacher? No, he's stiff and not very personable. That said just because he isn't anybody's best friend doesn't make him lousy. I get people have complaints he wasn't more attentive or sensitive to Momoko but keep in mind again he doesn't know all we do and he's a guy doesn't want to seem partial. Moreover, he's human just like everyone else. He won't necessarily notice (or appropriately understand) every little thing that's going on and she's not his only student. Teaching is a hard job, and I imagine its not easy to find the perfect balance between being supportive and still enforcing discipline, especially if he's not naturally a warm person. Are there ways he can improve? Sure of course, but personally I don't think he deserves to be condemned just because he isn't as likeable. I would like to see him have some character development but I don't think we're at that stage yet. I think the author is letting us get a feel of the characters as they are now and how they're connected.