Of course it's not easy when your ethical standards are questioned - particularly not if your own family gives you that challenge. It's hard to get people of that age to listen - particularly as a parent.
Based on your definition of a good citizen, it seems that both you and your son live up to your standards.
How did the school react? Here in Austria, the ministry ruled that students' attendance of Fridays for Future is not to be counted as an excuse for their absence. A move that, in my opinion, shows helplessness and a lack of actual willingness / the ability to start a dialogue with our youth...
RE: CIVIL DISOBEDIENCE - FRIDAYS FOR FUTURE