The first trick is to get a circle of about 10 kids around and about 5 kids deep. This is vital as it blocks the adults from getting to see what is going on and to prevent them from getting in. The participating girls throw their panties to some lucky fellow and the girls in the middle actually DO sex acts with the boys to the beat of the music. The sex acts range from oral to well...whatever. When there are no panties, the field is wide open.
...And before someone starts in on "those horrible public schools" this was at a very tony private school where the tuition is on par with ivy league colleges.