Pile a few kids in the back of your car and ignore them. Put on some quiet music and appear absorbed in the music or your driving. Then listen up. You are sure to hear about teachers, playground events, bullies, friends & more.
Hear something that concerns you? Later, much later, (so they don't remember that you were driving AND listening) bring up the topic for discussion with your own child. Heard something unexpected about another child? Unless that child is in danger, keep it to yourself. Never call another mom and tattle about antics shared by any of the kids. Remember that you are hearing things from a child's perspective.
This method is a safe way to check in with what's happening at school, without your child even being aware.