I understand the blunt. That's me. I had a 2 hour IEP meeting with a very large group of people and it got heated at times. Luckily, my husband was there to balance me out when I was to over the top

. So the only advice I can give is to stay calm and use education lingo. If you are in a state with some protections they will likely have the word "appropriate" in their mandates. They will also understand FAPE-Free and Appropriate Educaiton.
I just keep going back to the phrase, "I know we all want to see DS6 get an appropriate education." and "As part of DS6's free and appropriate education, I'd like to see him working on a level he hasn't already mastered 2 years ago." Stating it this way they couldn't help but agree. I mean what could they say. No I don't want him to have an appropriate education. Or worse. No I want him to work on something he's already masterd. LOL. Now that would have been hiliarious!
I digress. Basically I kept it logical, as much as possible. They understand numbers, statistics you can prove, laws and regulations of the areas, and educational research you can quote.
Good luck!