To a hammer, goes the saying, the world is a nail. Perhaps to an economics writer, even a distinguished one like David Leonhardt of the New York Times, the world is an economics equation. And perhaps that is what has led Leonhardt astray in a post to the Times' Economix blog, "The Declining Payoff From Black Colleges."

Leonhardt's "Declining Payoff" post responded to reactions he received to a previous post, "Revisiting the Value of Elite Colleges." In the course of reporting that research indicated that most graduates of elite colleges like Harvard and MIT don't make higher incomes than those who graduate from good but non-elite colleges, Leonhardt noted that the rule did not seem to apply to "black students, Latino students, low-income students and students whose parents did not graduate from college," for whom attending an elite college appeared to translate into higher earnings. "Students who choose a historically black college over an elite college," he wrote, "may be hurting their future earnings potential."

In his "Declining Payoff" post, Leonhardt doubled down on his argument. "There's more evidence for this finding than I knew," he wrote, citing a study by economists at Harvard and MIT. Much further down in the post, he includes the caveat, "Of course, wages are just one measure of a student's satisfaction with a school."

Now, that should have been his headline: Wages are, indeed, just one measure of a student's satisfaction with a school. And they are just one measure of a college's importance, not only to the students who attend it, but to the society at large.

Take the group of students that Leonhardt refers to in the first post: black and Latino students, low-income students and first-generation learners -- students whose parents did not graduate from college. For how many of them is attending an Ivy League school a realistic option? Yet, those are the students most in need of a college education, and whom the economy and country most need to get one. With the economy's growing need for college-educated workers, and with significant percentages of higher-income students already on track for college, those are the groups on whose education we need to focus.

How well-positioned are elite colleges to fill that need? In fact, they enroll a very small proportion of students from low-income families: Washington University, just 6 percent, for example; Vanderbilt University, 8 percent; and Duke University, 9 percent. By contrast, two high-performing HBCUs, Xavier University of Louisiana (the nation's top producer of African-American medical students, and one of the top three producers of African-American pharmacists) and Atlanta's Morehouse College (Dr. Martin Luther King Jr.'s alma mater, and my own), regularly enroll eight times the percentage of low-income students accepted by Washington, Vanderbilt and Duke.