As Kevin Gaines discussed the history of the civil rights movement in a University of Michigan class recently, he said he found himself looking at 15 white faces and two African-American faces.

That lack of diversity made having robust class discussions difficult, Gaines, a U-M history professor, said Thursday during a conference call with reporters.

Gaines is a plaintiff in a lawsuit seeking to overturn Proposal 2, a Michigan constitutional amendment passed by voters in 2006 banning the use of race in admissions decisions at public universities. The case will be heard Tuesday by the U.S. Supreme Court....