OP, your state does not have a (meaningful) gifted mandate, so I wouldn't expect too much from GT programming. OTOH, MA does have excellent access to resources outside of the schools themselves, of which more in a moment
There are a number of well-known high-achieving prep schools, which might suit your DC at a later age, pending EF skills, but which would be even more likely to be helpful if he were a little lower LOG. To my knowledge, there are two more-or-lesss GT privates, which run about a grade level ahead--not enough to truly meet your DC's instructional needs for the long term, but maybe an option short term. If you can find a tiny private that fits your family's values, sometimes you can talk them into some flexibility (we did that for several years, with a pathway with some similarities to Kai's DC, prior to homeschooling #1--early entered to 1st, skipped 4th on a school change to a different tiny private, additionally SSA in math and English in 5th and 6th, exited to homeschooling after 7th).
MA also generally allows homeschoolers to use the instructional and extracurricular resources of their LEAs (public schools), technically at the discretion of the district, but in practice usually everything up to just short of all core classes (this last to avoid parents enrolling their children as "homeschoolers" who attend school all day but are exempted from state mandated standardized testing). So your DC could attend just, say, gym, music, art, computers, as a homeschooler (as long as you can transport), and do all academics at home (we did this with DC#2 at the second tiny private).
MA, like many other states, allows for dual enrollment at all public CCs and most public 4Y universities for public, private, and homeschooled students, with the permission of the school admin (or the homeschool approval letter of the LEA).
To that point, MA also has surprisingly little regulation of homeschooling, requiring only a letter of intent to the superintendent or designee of your LEA. Some districts may request additional information about your educational plan and student's yearly progress.
In addition, MA has two virtual charter schools, one of which uses K-12 paper curricula, and the other of which uses Connections Academy online curricula. Some limited flexibility in placement is allowed, and, of course, both are self-paced, so you could always race through the assigned curriculum at whatever pace suits your DC, and then spend the rest of the time exploring fun, interesting topics.
Outside of school (of any description)-based programming, MA, of course, has many historical, cultural, and artistic opportunities, which you could use for deep and authentic multidisciplinary learning. Also, a rich pool of highly-skilled professionals in many domains, which you might be able to tap into at some point for a mentor.
More info:
http://mhla.org/
