I think to say Sheff vs O’Neil only focused on Hartford misses a good chunk of the picture.
The main instrument to address the ruling was the development of magnet schools. These schools were designed to draw suburban kids into the city. A magnet school often has a special theme and the states spent hundreds of milliosn building them out.
There are 44 magnets in CT. Fifteen in the Hartford area, Twelve in New Haven, three in New London, and three in Bridgeport.
I have no data but I think the biggest driver for magnet enrollment is free full day preK and Kindergarten.