Another manga I've read a long time ago and looked around for has escaped me when it comes to the name. I've seen others called Muranase!, Animal Academy, School in the Wild, and a few others, but they just aren't it.

The manga I'm remembering is about a young male teacher that was supposed to be teaching at a normal high school (either that or he was transferring into another one in the area), but he ended up somewhere in the mountains, finding a place mostly inhabited by animals / animal people. He either got caught in some odd weather and had to stay there, or he just transferred there by accident - either way, he ended up staying with these kids and trying to teach them (some were difficult about it). The most I can remember is that there was a squirrel boy, and maybe a fox or a dog? One of the animals, probably the fox/dog, actually ended up really disliking the teacher at first, possibly because he was a human.

The teacher had ended up leaving the school at some point, I think, to go and teach for a normal school... either that or he left for a short period of time, but he ended up going back to his animal school at some point or another. Pretty sure that to the outside world that place was either a secret or it didn't exist at all whatsoever.

There's Gakkou no sensei and it's shounen-ai.