24/15 is pushing it. you'll see 24/17 at any random trip to the mall. it's really not a strange thing. it's never been a strange thing.
one thing you could do is increase the educational requirements to get a teaching job. maybe teachers should have masters degrees.
but i don't see how you can expect anything different when you put 23 or 24 year old teachers in a senior high school classroom. that's like putting dogs in a room and locking the door.