That's about how teaching methods are failing some children, and then they're being judged for it unfairly. It's not against proper education and testing and using that to sort.
if you assume that all children are equally capable of learning everything then you are forced to conclude that teaching methods are failing some children. But if you "believe in science" (it's quite popular today to profess belief in science), you don't believe assumptions like that.
All children are equally capable of learning but different children are receptive to different teaching styles and approaches.
Only teaching children with a small selection of approaches that were primarily refined with middle to upper class white neuro-typical children can be considered discriminatory.
That's the point of those studies.
It would be like forcing a kid who is growing up in middle-to-upper class western society to solely learn mathematics via ancient greek visual proofs and then blame them for not understanding maths because they "just aren't trying" or "they aren't smart".
Everybody has equal capacities to learn but only if you can find the style of learning which works for each person.
Economic status and two-parent vs one-parent households are both stronger indicators of educational achievement than pretty much any other, including race.
However, when broken down by race, economic status is heavily weighted by race in America and Canada (differently in each country, but but still present).
One can’t simply assume spherical cows here, because there is a deeply historic, systemic, and persistent imbalance which gets compounded through chronic underfunding of economically depressed (and mostly minority) education systems. Some of the systemic racism is ongoing and being actively encouraged by bad actors who misuse the words of Dr King to oppose real measures that would begin to address these imbalances.
That's about how teaching methods are failing some children, and then they're being judged for it unfairly. It's not against proper education and testing and using that to sort.