Sorry Agent, but I'm a sub and I can get the highschoolers to be quiet for announcements.
I'll admit that there aren't 30 to a class yet, but there are as many as 24.
If the girls are mumbling then they should be taught to speak clearly. I know plenty of guys that mumble too. I find it very hard that a school would actually implement this policy at all... Are you yankin' our chains?