Say that you apply to many schools, including some where other students have much better predictors (chiefly test scores and grades from earlier institutions) than you. And you get in! Maybe it was affirmative action (whether based on race, socioeconomic status, or something else), maybe it was a preference because your relatives had gone to the same school, maybe it was something in your admission essay, maybe it was just luck. Either way, you’re thrilled.
Might you have reason to be less thrilled, and actually not want to go to this highly ranked school? (Conversely, might the school reconsider its policy that led you to be let in?) If the predictors are actually reasonable predictors (and apparently grades and test scores tend to be reasonable predictors), then you can expect you’ll end up lower in the class at the new school than you might be at some other school, precisely because the other students are better than you. The advantage of having a more prestigious degree might be counteracted by the disadvantage of having a less prestigious class rank. But might you end up getting a worse education, being less likely to graduate, and being less likely to pass any professional licensing exams (such as the bar) that you might be expecting to take?
That’s the debate about the “mismatch effect,” which I’ve followed over the years (though from a distance); it has mostly focused on whether race-based affirmative action causes problems (such as lower black bar passage rates) as a result of this effect, but it can also be relevant to many students of all races. I was first exposed to it because of the work of my UCLA School of Law colleague Rick Sander, and Robert Steinbuch at Arkansas / Little Rock has been working in it as well; Rob has been kind enough to pass along these thoughts on the subject: