I have come out as non-binary twice to teachers.
The first time was when my Human Relations teacher was talking about the differences between men and women and decided to have people split up by male/female. I was already pretty upset that day, so basically I just did nothing until my teacher got angry with me for not participating and I started crying. So I told her why and she said she was supportive of that and that was pretty much the end of it
The second time I can't actually remember what prompted me to (even though it was only like a week ago), didn't really get a reaction. Not in a negative way, just isn't a big deal to her I guess.