For many years, diversity in higher education has been measured by how many low-income students and students of color enroll in college. The Bill & Melinda Gates Foundation wants to make a dramatic change in that definition, by focusing instead on college graduation rates.

The foundation, along with the National League of Cities, announced Monday that New York City; San Francisco; Mesa, Ariz.; and Riverside, Calif., will each receive $3 million over the next three years for work designed to boost college graduation.

The foundation says its long-term goal is to double the number of low-income adults who earn a college degree or credential that meets job-market demands by age 26.

The grants announced Monday are for aligning academic standards between high school and college, strengthening data systems, implementing early assessment and college prep strategies and creating support systems to help students get through school.

In announcing the grants, the foundation pointed out the following statistics about the cities where the money will be spent:

— Low-income students who graduate from Mesa Public Schools and enroll at Mesa Community College have a 5.4 percent graduation rate.

— Ten percent of the students enrolled as freshman at the City University of New York in 2006 had earned an associate's degree three years later.

— Riverside City College has a graduation rate of 14 percent.

— About 27 percent of 9th-graders in San Francisco will go on to earn a post-secondary credential or degree.

"We know that in today's economic climate and labor market, a high school diploma is no longer enough," said Allan Golston, president of the U.S. Program at the Gates Foundation. "We must not only ensure that young people have access to college; we must ensure that they go on to complete college and earn a degree or certificate with value in the workplace."

Since 2000, the foundation has spent $5 billion on its efforts to improve American public schools, send kids to college and, over the past few years, improve college graduation rates.