I have a question about joint legal custody and decision making.

I have residential custody of my kids and ex sees them a few weekends a month. We have joint legal. The kids are very young. I am wondering about decisions about the kids' education and medical stuff in the future and tie breaker status. When the kids get older, if for example I thought one of them needed to go to a psychologist, and my ex and I and I disagreed, whose opinion would win out. Would I have to take it to court to be able to take him? Or would I get the tiebreaker? Or would I take our child and it's up to my ex to contest it in court? We do try to compromise on issues but as the kids get older I think there may be more issues and my ex is a difficult person. Our agreement says that we have to 'consult' on medical and edu issues, not that I have to get his permission...