Some states, like where I am in Illinois, have all party consent laws. I can tell you, based on my experience volunteering at local schools, there would be multiple parents in every classroom who would not sign consent. In my town at the beginning of each school year, we also have to give consent for pictures taken by the school to be used on the website or any publications (or parents at classroom parties who then give the pictures to the teacher to post on their website)--and in every class my kids were in, were at least 2 parents who did not sign that (for various reasons). Obviously it would be for internal use only, but I knew some of those parents personally, and I know they still wouldn't sign consent for permission for a classroom camera. And you couldn't just position the camera so it didn't record the kid in their seat--kids in classrooms are always getting up to talk to the teacher, go get supplies, put something in the trash, etc.
Picture walking into your child’s classroom and noticing a small black camera mounted in the corner, its red light blinking steadily.
medium.com
Alabama mandates cameras in special ed classrooms, while Georgia’s Landon Dunson Act enables video monitoring in special education classes. Florida, Louisiana, Nevada, and Texas legally permit cameras in certain classroom settings, particularly for protecting vulnerable students.
"Texas generally prohibits recording in spaces with “reasonable expectation of privacy,” though exceptions exist for special education classrooms with parental consent.
Michigan generally prohibits classroom cameras entirely. New Hampshire has stricter laws around hidden surveillance."
The article also talks about the tricky issues surrounding using school video recordings in disciplinary actions in regards to FERPA.