Between 1955 and 2005, college enrollment in the United States exploded. This should have brought with it a great increase in social mobility, lifting millions up out of their economically tenuous origins.

It didn’t. And now Sigal Alon, a sociologist from the University of Tel Aviv, is attempting to explain why:

The key factors, she writes, are that demand for higher education outpaced supply (even with all of that growth in available slots), that testing became a more important factor in admissions at more institutions, and that wealthier families are much speedier to adapt to changes in admissions rules.

While the findings make her sympathetic to some recent trends in admissions — such as the movement to go SAT-optional — they also leave her skeptical that such shifts will be enough to change class divides in higher education.

Alon’s study is based on three large national surveys of students that provide data on what happened to the high school graduating classes of 1972, 1982 and 1992. She finds that much of the growth in enrollment of students of lower income socioeconomic groups came at two-year colleges, while gains at four-year institutions over all and selective four-year institutions were quite modest.

During the 1970s, she found, there was more progress, and this is a period when colleges that greatly expanded capacity (individually and in their entirety) during the 1960s to meet swelling enrollments found a dropoff in the number of new applicants. From the most elite institutions to open admission colleges, institutions became less competitive — and the ability of low-income students to get in grew.

But from the 1980s on, that stopped happening. During that period, she writes, the trend was one of greater emphasis on standardized tests — not just at the most competitive colleges, but across higher education. While this process was gradual and started before the 1980s, it took off then.

In more recent years, she notes, tutoring and coaching services have proliferated, and the correlation between SAT scores and family wealth has been consistent. Beyond the obvious economic issues at play, Alon writes that this is part of the sociological theory of “adaptation.” Parents of all economic classes want their children to succeed, but the wealthier ones “better understand the postsecondary landscape and competitive admission process and they invest in resources to promote college attendance,” she writes. As a result test score gaps of high school seniors — grouped by economic background — have grown during recent years.

Alon writes that as long as college admissions remains competitive, such trends will continue — with wealthier parents finding ways to improve performance for their children, no matter what measures colleges use to sort applicants.

This explanation is pretty elegant in its simplicity: Richer families will simply always be better able to game the application process, whatever it entails, skewing the numbers of each incoming class. Alon’s work is certainly a strong point in favor of affirmative action, both class- and race-based, given the huge wealth discrepancies—many of them race-related—that persist in this country.

Jesse Singal

Jesse Singal is a former opinion writer for The Boston Globe and former web editor of the Washington Monthly. He is currently a master's student at Princeton's Woodrow Wilson School of Public and International Policy. Follow him on Twitter at @jessesingal.