The problem is that A. they called it "gifted" so people thought it was something you _wanted_ your kids to be and B. the screening test they used was the IQ test, which you can massively improve your score on by studying for it. So parents were determined to get their kids into "gifted" education, and coached their kids on the tests to get in, and in the meantime kids from less-privileged backgrounds with the same characteristics were being labeled as behavioral problems and shunted into remedial programs.
Now that we have the label of "neurodivergent", it seems to me it would be productive to reframe "gifted" education as "neurodivergent" education: rich parents would stop trying to get their kids into it, and it would be able to serve the kids it was intended to serve.