In my experience inside the schools, we've usually acted on current neuropsychs being sent in by convening an IEP team, without going through a fresh evaluation. The systems I've worked in have responded to the letter requesting eligibility determination, with accompanying completed eval, by scheduling a team meeting within 15 school days, much like they would do on completion of an in-house eval. Usually, a determination (and plan, if warranted) would be made and developed at that meeting. Occasionally, the team might suggest additional assessment before making a final determination, or write an 8-week extended eval IEP (tentative determination of likely eligibility, with services to be refined pending additional evaluation). (Technically, the IEP doesn't expire after 8 weeks, but the team is required to reconvene to discuss the additional eval info within 8 weeks, at which point the IEP is finalized.)
It doesn't sound like your school is quite as responsive as the places I've worked!
I still think your request for IEP eligibility determination should most appropriately be accompanied by the neuropsych report, especially as it should speed up the process (saves you the 30 school days of time line allowed for conducting an eval). You could consider having the psych write up a compact cover letter that succinctly lists the type of accommodations they recommend. I stress compact & succinct, so there is no question of overlooking critical items, or getting bogged down in psychspeak. Although those should already be listed in the recs at the end of the report.
If you give them the report, they will have the accommodations anyway. Then you can discuss them again during the meeting, without anyone feeling blindsided.
The letter and the neuropsych should go to the IEP adminstrator in your building, who may be the SP, school counselor, special ed teacher, or a dedicated special ed administrator. If you can't figure out who that person is, ask the school counselor or school psych where you should direct your letter. Or if they can't/won't help you, send it to the district director of special education.
In a 2e situation, the main difference in your letter will be that your concerns are about relative underperformance, not about normative underperformance. The amount of emotional distress and effort that he is having to put into achieving at his current level, and inconsistent performance that may be related to a disability are other concerns you might have. These are actually commonly associated with IEP-eligible disabilities, even in those of average cognition. Basically, if you think they are going to scoff at the academic underperformance piece of things, you'll want to emphasize the latter two items, or related concerns.
