Hoxby said that "the main group of students who appear to be getting displaced from very expensive colleges is the group of students from medium-high to high-income families who have low college preparedness."

Prepared students from lower income families are replacing them, she said.

According to a news release, the Senate hearings were scheduled because Americans are increasingly concerned about high tuition costs.

Over the past two decades, tuition has more than doubled at both public and private colleges. And tuition rates have risen faster than grants, loans, state appropriations and other subsidies.

A report by the American Council on Education indicates that 71 percent of Americans believe "a four-year college education is not affordable." The cost of a college education is a top concern for 65 percent of Americans--putting it ahead of violent crimes against children, children's health care and the quality of public schools, the release said.

The presidents of Connecticut, Macalester and Rhodes Colleges also testified at the hearings, as did education authorities from various national organizations.

Witnesses at the hearing also discussed "merit aid," a form of tuition discount that allows students to bargain for prices lower than those advertised.

"Apparently, colleges and universities themselves don't have a good understanding of why tuition rates are rising so rapidly," Thompson said. "Colleges have to do more to make themselves more transparent in explaining their finances."