With 30 students and a teacher in each classroom, just what privacy would one expect? Seriously, there is no privacy in school, except maybe in the bathrooms.
A little paranoid about the videos? A system could be set up that was internal only. And if nothing happened that day, all videos get deleted. Really not a big deal and it certainly would create a less disruptive environment in the classrooms.
I do understand your position though and said that not everyone would like it......it is an option though.
But with a camera, The school would know who did what and to whom. Neither side could get away with anything......