Affirmative Action, Richard Sanders and Thomas Sowell
Sanders' explanation is a mismatch between students and schools. Black students do not, on average, end up in the same law schools as white students with the same credentials. Law schools compete to get black students, there aren't enough well qualified ones, so elite schools accept black students with qualifications well below those they require for white students. The result is that many black students end up in schools and classes they are not qualified for, learn little, and fail to pass the bar--students who would have done better in a less elite school designed for students more like them. He estimates that a race blind admission policy would result in fewer black students going to law school but more passing the bar.
After reading the op-ed, I told my wife about it. She pointed out that the argument was not original with Sanders. Almost twenty years ago, in his very interesting Choosing a College: A Guide for Parents and Students, Thomas Sowell made precisely the same point in the context of colleges rather than law schools. Black students at MIT had math scores well above the national average but far below the average for white students at MIT; they would have gotten a better education at a less elite engineering school.