The German drum circle organization, percussion m+, founded by Remo Endorser Mathias Reuter, did a wonderful Drum Circle School Project in Prague (DSP School Prague / "Jugend musiziert") with more than 200 kids, ages 5-17 years old.
They started by facilitating small group of 20 children in a one and half hour drum circle workshop and these kids became the "assistants" of the large event that followed.
They set the chairs and instruments, and have rhythmical support to the larger group and knowing the fundemental drum circle elements, also did some basic facilitation during "jump time", which is an opportunity for facilitators to "jump into" the middle of the circle.
This is one idea for facilitating drum circle in schools, and anywhere else for that matter. It really works!