It's not just a principal/admin that should insist upon this. It's state law.

ALL communications to students should be done in full view of their parents. If it isn't, a case could be made that there was an "attempt to conceal" the contact and that's grounds for prosecution.

ALWAYS be as transparent as possible. Don't give a student OR a parent your personal cell number, EVER. (Use Google Voice, which logs all communication including text messages).

Shield yourself from liability.