Access to high-quality education is unequal from earliest schooling, and over time, those inequalities build on themselves. Community colleges have contributed to this problem, but they are also essential to the solution.

Regardless of previous academic achievement, low-income students are much more likely than higher-income students to attend community colleges than four-year institutions. And students who start in community colleges do not, on average, progress as far as those starting in four-year institutions; they are certainly less likely to complete a B.A. Thus, by starting at a community college, they may fall further behind more-advantaged students.

Research suggests that many low-income students are "underplaced": They have the academic skills to gain admission to more-selective colleges than the ones they attend. Better counseling and financial-aid programs might improve equity by displacing some higher-income students from four-year colleges. But it is hard to believe that such efforts would make a perceptible dent in the current extent of inequality.

Eliminating community colleges, or encouraging every student to enroll in a four-year institution, won't work unless four-year institutions are willing to take the students who now attend community colleges. But selective institutions are not about to open their doors to all comers. For the most part, they have used the growing demand for higher education to become even more selective rather than to expand enrollment.

The availability of low-cost, local, open-access community colleges is therefore crucial. As tuition at four-year institutions rises, and college degrees become a prerequisite for jobs paying a living wage, community colleges fill an ever more crucial role in our economy. Accordingly, their enrollments have steadily grown.

But fewer than two-fifths of students who start in community colleges go on to complete a degree or certificate within six years. Community colleges must find a way to increase completion rates without restricting access.

Can that be done? There is reason for optimism. The past decade has seen a growing volume of research, and reform, devoted to that issue. Perhaps the most important conclusion is that reforms must be ambitious and concerned with the entire student experience at college, including opportunities to transfer to four-year colleges. Reforms that focus on only one stage, such as remediation or counseling for course selection, will have, at best, only modest effects.

Right now, millions of students are enrolled in community colleges. Improving community-college performance will have a direct, positive impact on their lives and future opportunities. With enough improvement, community colleges may even become an attractive alternative for upper-income students.

Thomas R. Bailey is a professor of economics and education and director of the Community College Research Center at Teachers College of Columbia University.