Well, I have no idea if he's open to poly or not. He hasn't given me any indication that he is remotely interested in me. I wouldn't know how to go about asking that question especially since he is my daughter's teacher. He probably just sees me as another parent to one of his students.
That doesn't mean that I can't find him attractive but I don't think that it's fair to assume that he would welcome being asked out by a married woman without feeling awkward and thinking that I am a cheater. I also haven idea if he would want children but again I don't think it's fair to assume that he wouldn't. I am a worrier if you couldn't tell that, lol.