That's impossible to regulate... and could be a particular subject that is controversial, they have a policy that is as good as their superintendent. I think it is going to be really local, and age-dependent. Our high school classes were all about debating opposing views where there were any, and memorably among them, crevo theories.
Except that as educators we receive regular lectures on possible areas of lawsuit. I've discussed this with my brother and uncles who teach in public school here. They are bound by the threats of being fired or sued if they broach the wrong subjects. Granted, if the student brings up the topics they can discuss them. But, they still have concerns over being misconstued in those discussions.
For my part, I have monthly meetings which reinterate the things for which a suit can be brought. My issues are different from the public school issues here - but just the same - I have already inadvertantly stepped over the line and been reprimanded for saying too much.
My limitations mostly cover student's privacy. But after the first events I have pretty much clammed up about some things I don't think are wrong to discuss.
First thing I did, first week I taught, was ask a student on the front row of class to switch seats with a student toward the back of the class having vision problems. This is a no-no because the vision impaired student hadn't documented this problem with the disabilities office. I was told that because there was no documented disability with the one student that I could be construed as discriminating against and be sued by the student on the front row for asking him to move back.
I don't do that anymore.
I have several equally stupid stories in different areas of my teaching after only 3 years. And I have learned to just NOT do anything! It's much worse in public schools from what I hear from relatives.
I have been threatened with lawsuits by 2 students who legally had grounds. Three others have threatened suits with no grounds. That's a lot of suit threats in 3 years. More than the whole rest of my life combined.