aeh, your expertise has once again brought laser-sharp focus.
smile

purpleviolin, I'm so glad this gives you the "compelling new information" needed for further advocacy. Here's a round-up of posts on advocacy, crowd-sourced as parents contributed on this forum over the years: Advocacy as a Non-Newtonian Fluid. Remember, we cannot work "against" a school or district, we must work "for" meeting a child's needs (including correctly assessing those needs and determining appropriate supports)... in doing this we may "raise awareness" and provide "guidance" as to what various experts and the law have set forth.

Please share all information and discuss strategy with your son, proactively. This may entail several conversations. It is not unusual for a school or district to attempt a "divide and conquer" strategy. Your family members must all be on the same page. This may be especially crucial as your son is in high school and may be expected and/or required to self-advocate.