It already has been a factor, unfortunately. DD isn't a kid that (apparently) does College Board tests exceptionally well-- I'm not sure if it's the format, or if she still has safety concerns that ramp up her anxiety to performance-attenuating levels, or what. It seems quite probable, now that we have an N of two.

Anyway, she certainly scored 99th percentile on the PSAT, but because of the timing of her 3rd skip, she didn't get a 'practice' run at that one, and therefore that was her very first out-of-home, formal testing experience. She missed the cut-line in our state by about a single question, and there is NO question that if she'd made that cut, she'd be a major contender for NMS, given the rest of her resume and her transcripts. Most of her practice tests had been VERY comfortably above the cut line. Interestingly, at home, when she's been tested by teachers from school, her scores are stellar relative to practice, so I do think that unfamiliar environment and disability-related anxiety is a major part of the performance attenuation happening. I am not entirely sure what the acceleration has done there.

As you note, the alternative to having that additional acceleration is virtually unthinkable either way.

Her scores are high enough for all but a tiny handful of institutions, and I'm not so sure that she wouldn't be competitive there, too,

The short answer is that yes, there MAY be some impact on test scores, but it's hard to say what it is. In practice that seems to have meant that on any given day, DD's SAT scores are "above 700" rather than higher. She has only taken the SAT once, and honestly, her endurance is part of the problem with that one. In light of that, we've determined that having her take the SAT again probably wouldn't matter. Sure, her math and writing scores might be higher, but she's unlikely to top the reading score that she has, since it's already near 800. On any given day, though, the math or writing COULD be higher quite easily. She's definitely hit repeated home-runs on the writing, scoring 800's routinely in practice exams. The SAT is a grind-- maintaining your focus on something that is inherently not that challenging or absorbing, but IS that stressful, over the course of 5 hours is-- a bummer, to say the least. Especially when you're done with each section in about 1/3 the allotted time, and just get to SIT there doing NOTHING while time runs out, which is what happens. Even if you test with accommodations or individually-- you sit for the full time allotment in each section.

Given how HG+ kids read multiple choice exams that are written for bright but NT people, 'perfect' scores are not necessarily a given no matter how capable the individual is, anyway, and so it may be that waiting to take them as an older student wouldn't really be helpful anyway. DD did a lot better on SAT practice done for fun a few years ago than she has in the past 6 months, when they 'counted.' As she grows cognitively, it gets harder to read those questions as-intended.

In my opinion, and this may only apply to kids who are EG+, I don't know-- it's probably a wash whether acceleration helps them or hurts them in terms of SAT performance. The further they go "past" NT for that cohort, the harder it may be to read superficially enough to get near-perfect scores. On the other hand, more life-experience means better executive skills, etc. which improves that 'on-demand' focus and ability to get inside the internal logic of the test.

We're thinking that the ACT probably would have showcased her better, being both shorter and not as choppy, as well as having a science subsection, but seeking accommodations complicates things substantially for her and frankly I'm not able to do it again just for the ACT-- too much energy output. If she does take the ACT, I've already told her that she'll have to do it without accommodations and hope for the best. Not ideal.

That brings up another really good point, though, and that is that for 2e parents-- you MUST make sure that your IEP/504 is both current and adequate to gain your child the accommodations that s/he needs in order to take those standardized tests. Do not assume that it's a given just because the school has been doing them, and allow at least 3 months to get them squared away with College Board or ACT either one.

Schrödinger's cat walks into a bar. And doesn't.