You won’t change a whole school at once. Change one person’s mind, then ask them to help with the next.

Big change looks like one event, but it is almost always a chain of small private conversations nobody wrote down. One person convinced and then recruited is worth more than a hundred who heard an announcement, because they bring their own circle with them. Starting small is not lowering your ambition, it is the mechanism.

Choose the single person whose support would matter most and talk to them properly, not in passing. Then ask them who to talk to next. Keep going until the thing has more owners than just you.