Okay, so it's good you identified him as a trigger. So now to set up coping skills.

I'd say first make a list of all the things he does that trigger you, and then come up with pre-planned reactions. For example, knowing he's inflexable in advance can help you because you can set up a game-plan before you talk to him about anything. You can plan out exactly what you want to say, do not deviate from it, and once you've said your piece say goodbye and walk away.

Same with knowing he needs to have the last word. Know it in advance so that you're prepared for it.

If the coping skills don't work, maybe send your husband to deal with this particular teacher instead. Show him that you're a unified front for your child's education.