I don't have group data on that, just anecdotes. I'd guess more than 0.1 %, though. I do know that Brookline is among the systems that actually has a protocol (or did at the time) for early admission to kindergarten, heavily weighted toward the cognitive assessment. (WPPSI and WJ achievement, at the time.) And that some kids were able to get gifted pullout in elementary on the basis of an interview, history, and observation, without testing. Of course, it's been a few years, so things could have changed.
I'm afraid they have. A colleague is sending his gifted daughter with an October birthday to private school for KG and 1st grade because the Brookline public schools will not let her into KG before age 5.
Boston assigns children to elementary schools based on a lottery system
http://www.bostonpublicschools.org/assignment , so your child may not get into the nearby school. My colleague did not like this, which is why he moved to Brookline. In general, affluent people either send their children to private schools in Boston or move to suburbs such as Brookline but do not send their children to Boston public schools.
