Boston University is among a list of private colleges being called upon to enroll more low-income students. A new study released Tuesday finds that BU, at 15 percent, has one of the lowest percentage of Pell Grant eligible students among the schools that were surveyed.

Georgetown's Center on Education and the Workforce says nearly 90,000 low-income students in the U.S, have the grades and test scores to attend selective colleges with high graduation rates, but don't. Instead, they go to open-access colleges, which tend to have lower graduation rates.

And the Center's report says many private colleges are posting annual budget surpluses and could enroll thousands more of these Pell-eligible students without hurting their bottom lines.

"There's more students from the top one percent than there is from the lower 60 percent of household incomes at a lot of elite colleges," said Martin Van Der Werf, who co-authored the report.

He says elite private schools are turning away too many high-performing poor students.

"Not every college student needs to go to a selective college in order to succeed, but the data shows you that if you go to a selective college, your chances of graduating are much, much greater," Van Der Werf said.

The study calls on private colleges to commit 20 percent of their enrollment to low-income students. Among the schools that are furthest from that goal: Boston University and Washington University in St. Louis.

UPDATE:  A spokesperson for BU says the reason the university is singled out is a factor of its total enrollment, not the percentage of Pell Grant recipients.

In a letter sent to the campus community Tuesday, Boston University President Robert Brown said ensuring access for all qualified students continues to be a major priority in the university's enrollment strategy and budgeting.

"Once again we have raised the financial aid for our incoming freshman class by 3.4 percent, with a focus on relieving the debt levels of students from the lowest income families," Brown said. "As a result of this commitment to financial aid, we expect to welcome a larger number of first-generation, low-income, and underrepresented minority students to our freshman class in the fall."

Related: New College Cost Calculator Boosts Applications From Low-Income Students