That's one thing that can shock parents but the school follows their evals and considers an outside eval. Outside experts in person at a meeting - same thing. They will follow what their staff says. Did they say no to an IEE at school expense? Tell them your child is bored and it going to be a behavior issue if his slow processing and ADHD aren't taken into account.
The 1st rule of special ed is to do it in writing (email is OK) so you have a paper trail.
I feel a 504 to accommodate the disabilities the outside eval found is a good 1st step. You can't force them to give your child an IEP & put them in the grade you want him in. An attorney & due process is the way to get them to do things.