If a teacher told me that I wasn't allowed to observe my DD at her classroom, I would laugh at them. If they didn't get the joke, I'd remind the teacher they work at a "public" school, and then I'd remind them of the public laws that guarantee me the right to access.

Such laws vary from state to state, natch, so I'd advise you to check yours.

And then, in a less playful manner, I'd ask the teacher why they think they should have unmonitored access to juveniles.