This study reports that between 1993 and 2008, there was a 7.5% decrease in the proportion of African Americans enrolled in U.S. law schools. The study also reports a 11.7% decrease in the proportion of Mexican Americans during the same period. (Hat tip: Brian Leiter)
I would guess the increasing importance of the U.S. News rankings explains much of the difference. A law school’s U.S. News ranking is heavily influenced by incoming GPA and LSAT scores of incoming classes. Given the well-known disparities of those numbers, schools may be choosing to emphasize the racial diversity of its incoming class less to get more of an advantage in the U.S. News rankings. Of course, different people will have a different sense of whether that is good or bad. But I think that’s the dynamic.