Give plenty of advance lead time when requesting amateur astronomer volunteers - several months ahead is best. They are in much demand by schools, and volunteer their precious spare time. Plan to have one or two telescopes for a school group less than 30 or so. It is nice to have a variety of telescopes to show different views. And be sure to instruct your students not to touch the telescopes unless the owner gives permission.
Some telescopes are rough and tough and user friendly, and like to be touched.
Some will be pushed out of alignment or damaged by the simplest touch. Find out what is up in the sky. The moon and planets guarantee a great viewing night, even if a light cloud cover is present. Light pollution from most school yard lights won't bother views of the moon and planets too much. Don't expect to see many deep sky objects from a schoolyard, however.