I’m substitute teaching now. I see hundreds of students a week. I have no idea who they are. I just have to get to know them on the run. Many of them dress gender neutrally now, and that’s fine, but if I want to refer to them in some way it can leave me with a problem, and I’ve run into it once so far.
It was a 4th grade class. Andy had a very short hair cut, cut up around the ears, jeans and a t-shirt, and converse tennis shoes. There was no clue whatsoever as to this person’s gender, except the hair cut. Andy lost their eraser. I asked, “Andy lost his eraser. Has anyone seen his eraser?”
Andy got upset because Andy is a girl.
How could I have found this out ahead of time? I can’t very well ask them directly because that would be just as upsetting, I assume.
I don’t want to ask other students for the same reason.

I’m stuck here! I’m in the middle of a whirlwind of 20 to 30 students who I don’t know, trying to get to know them, start them on a lesson, fielding them all at once so I don’t have the luxury of taking my time figuring this out about one student before I might (or might not) have a reason to address them.
I suppose I could refer to them as “they,” or “their,” but that would get pretty awkward pretty quick, I think, and would quickly send the same message that they don’t want to hear, that I don’t know what gender they are!

Any suggestions?