Personally, for a large group-like 500 0r 900 students I would send some sort of letter home first asking if they would like to participate, then pass out packets. That would be really expensive paperwork wise to make that many packets when for sure they are not all going to do it. Guaranteed...
The recipe is online now and when doubled fits in the large bar pan. They are very good and easy. I just had them at a show and garnished each square with a star of whipped cream, (with decorator) a fresh raspberry, and placed a few random mint leaves. They looked great!