Eugene Volokh has been all over the Supreme Court's split rulings in the University of Michigan affirmative action cases (just keep scrolling). I'll leave the constitutional theorizing to him, and will simply post here an excerpt from Justice Scalia's dissent in the law school case (the court upheld the law school's preference system while striking down that used in undergraduate admissions):

Unlike a clear constitutional holding that racial preferences in state educational institutions are impermissible, or even a clear anticonstitutional holding that racial preferences in state educational institutions are OK, today's Grutter-Gratz split double header seems perversely designed to prolong the controversy and the litigation. Some future lawsuits will presumably focus on whether the discriminatory scheme in question contains enough evaluation of the applicant "as an individual," ante, at 24, and sufficiently avoids "separate admissions tracks" ante, at 22, to fall under Grutter rather than Gratz. Some will focus on whether a university has gone beyond the bounds of a " 'good faith effort' " and has so zealously pursued its "critical mass" as to make it an unconstitutional de facto quota system, rather than merely " 'a permissible goal.' " Ante, at 23 (quoting Sheet Metal Workers v. EEOC, 478 U. S 421, 495 (1986) (O'Connor, J., concurring in part and dissenting in part)). Other lawsuits may focus on whether, in the particular setting at issue, any educational benefits flow from racial diversity. (That issue was not contested in Grutter; and while the opinion accords "a degree of deference to a university's academic decisions," ante, at 16, "deference does not imply abandonment or abdication of judicial review," Miller-El v. Cockrell, 537 U. S. 322, 340 (2003).) Still other suits may challenge the bona fides of the institution's expressed commitment to the educational benefits of diversity that immunize the discriminatory scheme in Grutter. (Tempting targets, one would suppose, will be those universities that talk the talk of multiculturalism and racial diversity in the courts but walk the walk of tribalism and racial segregation on their campuses--through minority only student organizations, separate minority housing opportunities, separate minority student centers, even separate minority-only graduation ceremonies.) And still other suits may claim that the institution's racial preferences have gone below or above the mystical Grutter-approved "critical mass." Finally, litigation can be expected on behalf of minority groups intentionally short changed in the institution's composition of its generic minority "critical mass." I do not look forward to any of these cases. The Constitution proscribes government discrimination on the basis of race, and state-provided education is no exception.