“Off topic: I know there are/were times that the school took the children outside to wait for moshiach.”
I’ve never experienced that, and the only place I can see that happening is a preschool but ok.
“Don’t you believe in Eliyahu Hanavi coming three days before Moshiach?”
I actually taught a class on that based on a sicha where the Rebbe brings in all the relevant sources. Your welcome to look it up yourself in the Seder shaarei geula- hoemuna vhatzifia, under the section on eliyahu hanavi. It’s on Hebrew books.org.
But basically, no he doesn’t have to come beforehand. As one proof you’ve probably heard of: someone who says they won’t drink wine, ie become a nazir the day Moshiach comes, is never allowed to drink wine because Moshiach can come any day. This is Halacha. Also one of the 13 ikkarim is to await Moshiach s coming every day, and if eliyahu hanavi had to come three days before, that would mean that we shouldn’t await him every day…