> You know nothing about teaching and education
That is incorrect.
> The reason why you group children with similar learning abilities together is so that they can progress together.
Yes, that's the thinking that justified tracking. Among the problems with segregated G&T programs, however, is that G&T-identified and non-G&T students are not, within each group, “of similar learning abilities”; Both have wide variation within groups, and individuals very often aren’t in the same relative position within their group in different specific subject areas.
As much as tracking would make (simple, binary) varying ability fit into the industrial assembly-line model of education, it doesn't work well with real people in the real world (it works very slightly better than the industrial assembly-line model without tracking, and when that was the norm, it was an improvement.)
But what works significantly better (though it takes more work) is to provide baseline curriculum with supplementation to individuals (in small groups of similar ability in the subject, where possible) based on ability. Which is what this proposes training all (initially) kindergarten teachers in, and hiring additional teachers in particular areas of need, in place of a high-stakes tracking exam for four-year olds. Its what has proven better than binary tracking in many places. (And it is, incidentally, what decided my family’s choice of schools for my son, who is now in kindergarten.)
It’s not the 1980s any more. Education has moved forward. Whether NYC will execute this well is, of course, up in the air. But that what it has identified is what has been widely used and proven better than binary tracking already, for the students that would be tracked into G&T, for the students that would not, for racial and socioeconomic class equity, and in basically every other conceivable manner is not up in the air.