What should I do about my son?

I need help, my sons father and I have been going through court for a while now. We have mediation scheduled in a couple months. Anyway a little back story, he has been fighting me on where our son will go to school. Neither of us live in the district that he continues to want our son in and it’s ranked way lower than where he could be. We had numbers issues with bullies at this school and our son would come home crying when I picked him up, he was spat on, pushed, made fun of etc. I was in the office multiple times over these instances last year. Well, we fought again this year because I wanted him to go to a better school (again) and he didn’t, the judge ruled to leave him where he is since it’s his last year. Well now this year our sin is acting out, not doing his work, grades dropping, just getting in trouble for things he knows better than to do. The part I need help with is instead of talking to our son ( we have joint custody) his father constantly tells him he is the bad kid, he is the problem that there are no bullies involved he’s just bad and doing it to himself. I kind of feel some type of way about this and don’t feel that constantly calling him a bad kid will fix any problems… I’m just not sure what to do, I can’t talk to his father about it with out him getting mad and arguing, I just feel stuck