I’ve never had a school segregate my presentation audiences by gender, but I know of authors who have experienced that.
I’m not aware of schools keeping girls out of presentations by male authors, only of hosts keeping boys out of female authors’ sessions.
For any author who wants to use it, I’m going to share the wording I include in the letter of agreement for my school visits. It is:
“Also, please note that I will not speak to an all-male or all-female student audience at a school that enrolls both boys and girls.”