Ban teachers from moving from the front of the classroom. Too many teachers are sexual predators and cannot be trusted to be that close to children. You teachers did this to yourselves. The world considers you abusive child sex predators now.

What about whenever concerns have been raised about specific teachers, for them to both wear a camera and have one trained in them secretly at all times

As I said, keep the camera trained at the front of the class or wherever the teacher sits. S/he might move around, that's fine. You can still hear what they're saying. If they do something untoward while they're out of camera range, hopefully the children will speak up or, if they are older kids, will have it on video themselves. There are far, far, far too many horrible teachers out there and there have been for decades. Time to take out the trash. Also, this doesn't have to be available to everybody, just school officials and parents. No need for every Tom, Dick and Harry on the internet to have access.