I can't speak to Boston particularly, but I have never seen a gifted program based any art of IQ test or proxy. In fact, I am almost sure that a vast number of people I knew in gifted programs, including myself wouldn't have scored particularity high on an IQ test. In fact I distinctly recall one gifted student asking me if their ASVAB score (commonly claimed by HN users and other to be correlated with IQ) of 20 was good.
Interesting, I grew up in Georgia and was constantly in and out of gifted classes from elementary school through high school. The process was very similar except there were basically no tests involved. In high school I was bumped to a gifted class randomly in the middle of the year without any additional processes.
I suppose it’s possible that that could have changed since I was in school, but it wasn’t that long ago either.