I have had this issue before where a simple question caused a teacher to become overly defensive. I do understand where they are coming from, but I do not think it helps.
Have you hunted around your district's website to see if there is anyone who is a Reading Specialist? Sometimes they can do a different kind of assessment that give you information on both decoding and interpretation, etc. If one of those exists, I think I would send a written letter asking them to do this. Even if this doesn't help this year, you would have the information for next.
You could also go up the ladder at school, above the teacher, and ask them if they can help you get your concerns addressed. You would have to word this carefully.
Their response might help you decide if you want to stick with the school next year or not, since it sounds like you have other options.
Good luck! It is not fun!
