Any law or policy that has a "disproportionate impact" on a protected class is subject to challenge, and will often lose in other public policy matters. I've not seen it happen in school demographics, though most, if not all, schools had some form of affirmative action policy until recently.

The "disparate impact" test applies mainly in civil rights act litigation, and it's extremely hard to make a case under that theory. It's a three-part test, and showing that a particular policy has a disparate impact on one race is just the first hurdle.

You also have to prove that the party acted with malice: either the policy exists for explicitly racist reasons, or the race-neutral justification is pretextual. If you can do that, you _also_ have to prove that there is a less-discriminatory alternative policy that achieves the same goal.

see, e.g., https://www.justice.gov/crt/fcs/T6Manual7#C'

It is definitely not de facto illegal to have a racially lopsided student body -- the school might be asked to justify the specific policy or practice that led to that outcome on race-neutral grounds, but saying "GPA and test scores" would be more than enough.

There is no disparate impact language in the civil rights title VI itself, but the language does appear in the enforcement regulatory frameworks issued by the federal agencies, including the department of education.

Title VI gives agencies authority to enforce Title VI, and many of those agencies added in disparate impact language into their own enforcement language (I think under the Obama administration, but I might be wrong about that).

Do you know what "de facto" means? I didn't say "de jure," and you're asking for de jure evidence.

It can only be "de facto" illegal if legal action was brought against some entity and succeeded, otherwise it'd be "de facto" nothing. GP also asked for an example case. TBH though I'm not how legal action would succeed without an accompanying law.

Any source at all here for your claim would be nice.