Look at it another way: Have black kids bussed into white schools had their test scores shoot up? No -- not even after decades of bussing.
Some black students -- in fact, whole schools of them -- have performed dramatically better than other black students and exceeded the norms in white schools.
Yet this phenomenon, which goes back as far as 1899 and included an all-black school within walking distance of the Supreme Court that declared such things impossible back in 1954, is totally ignored.
Are such things exceptional? Yes. But the mystical benefits of "diversity" are non-existent, however politically correct it is to proclaim such benefits.
Hard evidence shows that students of all races can succeed or fail in schools that are racially mixed or racially unmixed.
The latest variation on the theme of mixing and matching by race is that there needs to be a "critical mass" of black students in a given school or college, in order for them to perform up to standard.
Not only is there no hard evidence for this dogma, such hard evidence as there is points in the opposite direction. Bright black kids have benefitted from being in classes with other bright kids, regardless of the other kids' color.
All this is ignored in the Supreme Court's supreme farce.