May is when most college-bound students have to make their final decision about which school to attend. Students take a lot into account — from their parents' wishes to school rankings. Cost is a major factor, too. And that's an area where economists have a lot to say. This led a group of college-bound students to seek advice from a different type of college counselor, a renowned economist.The students were referred by the Matchlighters Scholars Program, a national program that pairs low-income, high-achieving high school students with free college counseling.Last month, the four high school seniors were introduced to their new college advisor, economist Caroline Hoxby. Hoxby is a professor at Stanford University and one of the world's foremost experts in the economics of education. The students were participating in an experiment where Hoxby was tasked with recommending the most economically sound college choice for each. She was given a list of their acceptances, proposed majors, finances, and the aid packages offered. Then, Hoxby told them her pick.One student, Julia Mueller, wanted a school where she could pursue her passion: " I'm a classical musician," Mueller said, "so the dream is to have a full-time orchestra job."But Hoxby cautioned that "90% of students in the United States switch majors." Hoxby said a university that offered flexibility was key, and she picked Duke University for Mueller because of its overall academic strength and potential to change majors. Recent education storiesFrom May 13: How a small college near Boston is serving low-income, first-generation studentsFrom May 7: As colleges sunset programs, what makes a major worthwhile?From May 1: For some families, new student loan caps are a big factor in college decisionsOften, students felt the lowest-cost school would be the best deal. However, Hoxby advised that "small cost differences are very likely to be dwarfed by differences in earnings."So what matters when choosing a college?"The one number that you want to look up," Hoxby said, "is what is being spent on a student in the college or university."Potential students can find this out on the U.S. Dept of Education's College Navigator website. The most selective American colleges spend upwards of $200,000 annually per student. Hoxby explained that this can be thought of as an investment in a student, with around a 5% return in future earnings. She warned that the biggest mistake students make is to pay for a school that doesn't invest highly in students. (Her research shows this is the case for many for-profit colleges, which can approach a 0% return.)But there’s another less statistical factor involved in successfully picking a college or university, she said: "It's important that you be happy."While students may be tempted to opt for the most affordable college option, economist Caroline Hoxby warns that it may not actually be the best deal.Dan Kitwood/Getty ImagesIan Chiba has lived most of his life in Texas. He received a good financial aid package from a large university in Texas. But Chiba wanted to move out of state for college to meet new people. "I think it's somewhat important for me to see different backgrounds and interact in healthy dialogues,” Chiba said. Hoxby recommended that Chiba accept an offer from Macalester College, because it appeared he'd be happier in that environment. She said that this would make it more likely that Chiba would take advantage of resources and finish in four years, because a delayed graduation date is an extremely high cost.Another student, Walter Giesen, was surprised when Hoxby recommended he attend Pomona College. It cost $35,000 more than his next choice but had a better alumni network in diplomacy and foreign service, areas of deep interest to Giesen. Giesen told Hoxby it was reassuring to know "that you see it as a smart move as long as I take advantage of everything there."Hoxby explained that students tend to be averse to taking out loans. But she said they shouldn’t be, because student loans — especially subsidized ones — are great deals.If you get one, Hoxby said, "march right down to the bank, put it in a savings account or a checking account that pays interest." She said that in this scenario, a student would actually earn money on the interest before having to pay back the loan, and they could hold onto the money until it was needed.Hoxby summarized her advice to students like this: "You should go to the most selective school where you are going to be happy."And guess what? Every student took her advice. This may mean that now, more than ever, students are thinking about the economic consequences of their college choice.Understanding the cost of college, with help from Marketplace’s “Financially Inclined”College is a financial decisionPaying for collegeTips for winning college scholarshipsMake student loans work for youFirst-gen finances