[user104658]

It's not illegal to record a conversation between individuals in a public place where there is no expectation of privacy. That would generally apply to a school, or even a workplace, although obviously workplaces can have separate clauses in the contract of employment regarding privacy and confidentiality (but it still wouldn't be illegal, just gross misconduct).

You can't record someone in a place where privacy is expected (like a toilet or changing area) and you can't record someone in their home. You might face civil consequences (get sued) if what you record and share with the public puts someone's reputation at risk.

Tl;Dr don't say anything controversial in a conversation with anyone unless you're happy with the risk of it being recorded and shared because no, it's not illegal to do so.