Not to mention that the possibility of a child seeing porn of their teacher is absolutely enough of a reason to say no.

I don't blame the teacher, but I'd prefer for the children to be protected in this circumstances. If it comes to securing the rights of a child or the right of an adult, I'll make my choice. Having young children access porn is abuse enough as it is. The potential that it's going to be someone they know in real life is even beyond that.