Re: MCAS. Yes to the untimed. (Or more-or-less untimed.) This is actually something to keep in mind as he goes up through the grades, as when it comes time for SATs, ACTs, or AP exams, he is going to need documentation, in the form of processing speed testing and accommodations on a 504 or IEP, to support the request for additional time (should that ultimately prove to be a functional concern). In the absence of routine timed assessment, you may not know that this is a potential concern for several years. And because MCAS is nominally untimed, you might not have documentation in any accommodation documents unless you ask for it. It needs to be documented in a 504 or IEP for at least a couple of years prior to the SAT/ACT/AP exams, or they will view it a bit suspiciously. So definitely pay attention to any feedback from teachers that might indicate functional impact from slow processing speed.
Also, not to downplay his outstanding performance at all, but, strictly speaking, a perfect scaled score doesn't necessarily mean a perfect performance, as there is usually a range of raw scores that can lead to the top scaled score, especially in ELA:
http://www.doe.mass.edu/mcas/2014/results/spring-conversion.pdf
