He "feels" he's right is the key point here.. He isn't doing research or thinking logically.. He's doing what pleases him.
You can't "feel" something being right. It can feel "good", but it can't feel "right"... sorry, but that's just BS
When he tries to argue just diffuse it :
You don't have any research to present to support yourself. You're just making this up and I won't waste my time on that nonsense.
You can argue all you want. Research from actual professionals says otherwise. And I am going to trust people who know what they're talking about.
When you have something concrete you let me know.
I don't have time to listen to you make stuff up.. I'm a busy woman.
You aren't right... You're just LOUD...
Being loud has nothing to do with being educated on this subject... A gorilla can yell... I want to understand that you have actually done a lot of research for your son... But clearly you haven't.
You can be loud with someone else... I am not going to expose our son to this nonsense.
Stuff like that.. Just DISMISS the argument rather than engage him.
When you argue with him you set boundaries too. Boundaries of fair debate etc... When he crosses a line there you call him on it and EXIT The argument immediately.
He will learn to argue fair or he knows you will just dismiss him and exit.
Each time he does it you call him on it again. Use the exact same words.
If he's just TALKING then cut him off there and tell him you will be happy to read anything he sends you but you aren't going to stand about and listen to him yell while he makes things up on the spot... etc
Just give him a simple response...
You can make all the excuses you want smart guy... No one is buying your BS... Particularly YOU.
"What is best for my kids is best for me"
Persevere = happily being patient over a long period of time