The problem with the G&T program was that it did a better job of selecting for parental affluence (the ability to pay 4-5 figures for test prep for your toddler, and the time to navigate a byzantine system) than for inherent differences in student capabilities.

Strangely enough, there were also a very limited number of G&T programs, including none in many of the poorer areas of the city, so if you lived in, say, the west side of the Bronx (as a friend of mine did) and wanted to send your kids to a G&T school, your best case was a 1.5 hour transit commute to East Harlem. My friend and his spouse could do that because they had work flexibility (including the flexibility for one of them not to work), but poor people don't usually have that either.

Effectively, this works out to socio-economic desegregation masquerading as racial desegregation (because, for various historical and structural reasons, race in NYC is correlated to affluence).