It’s September, and all across the country high school seniors are setting up their Common Application accounts, retaking SATs, and struggling to write (or procrastinating the writing of) 650 words that convey, in a tidy narrative, who they are, the challenges they have overcome in their 17 years on Earth, and why, Dear College Admissions Person, they really deserve to attend Your Excellent University!

Paul Tough is the author of The Years That Matter Most: How College Makes or Breaks Us. Buy on Amazon Illustration: Houghton Mifflin Harcourt

Depending on the circumstances they were born into, students might see these tasks as steps toward claiming a birthright or as giant obstacles that stand between them and a future of economic security. The former are helped along by tutors, consultants, and nagging parents; the latter scrape up money for test-taking fees and get what help they can from overworked school counselors. In his new book, The Years That Matter Most: How College Makes or Breaks Us, Paul Tough explores this divide, and interrogates whether going to college has become a privilege of wealth and whether it can still lift people out of economic insecurity.

Over six years, Tough visited big universities and small liberal arts colleges and community colleges, speaking with more than a hundred students. He writes movingly about students who are trying to navigate the confounding, expensive, and intimidating process of getting into and staying in college. Tough has written several books about education. This new book has some pretty depressing moments—especially about the current state of standardized testing. But he also finds plenty to be hopeful about.

WIRED: You've written a lot about education—about how important it is for children to have interaction in the preschool years and about teaching grit and perseverance in school. But this book, about what happens after K–12, is the one you call "The Years That Matter Most." Why does college matter more than those other stages of education?

Paul Tough: At its heart, this book is about social mobility: the ability of young people, especially those growing up in families without a lot of money, to improve their prospects as adults. When you look at the economic data, what’s striking about this moment in American history is how intertwined higher education and social mobility have become. The choices you make in the years after high school—and the choices that are made for you—are now more crucial than ever in shaping the trajectory of your life.

As to why this is true here and now more than at other moments: I think it’s mostly about scarcity. Because we’ve set up our system of higher education to be so competitive, so winner-take-all, those years have taken on outsize importance. A system of social mobility that puts so much pressure and responsibility on the decision-making abilities of millions of idiosyncratic 18-year-olds is not a particularly stable or effective one.

WIRED: What do you mean by scarcity? Certainly there are thousands of colleges students can choose from. Are you talking specifically about students getting into what are perceived to be the “best” colleges?

Tough: Yes. A distressing study by the Stanford economist Caroline Hoxby argues, pretty convincingly, that it really does matter where you go to college. The most selective institutions, she found, spend a lot more on each undergraduate than other colleges do, and they give a significant boost in lifetime earnings, on average, to the students they enroll.

I have to quickly point out to the nation’s stressed-out high school seniors and their parents that Hoxby’s finding was only an average effect. And the “best college” for any given student is still a subjective individual question. But Hoxby confirmed through data what many anxious students and parents and counselors suspect: Higher education has become increasingly stratified, with very different outcomes for students at different points on that selectivity ladder. That fact is at the root of that “scarcity” mindset. And it’s a problem—especially because those high-spending, high-mobility institutions are dominated by students from wealthy families.