The 16 schools lost 57 percent, or nearly 548,000, of their students who started classes in the 2008-2009 academic year, Harkin said at a Senate Health, Education, Labor and Pensions Committee hearing to examine the flow of taxpayer dollars to for-profit colleges.
He did not disclose comparable dropout rates for public U.S. universities or non-profit colleges, but public U.S. college and university dropout rates are as much as 50 percent, studies indicate.
More than 95 percent of students at two-year for-profit schools and 93 percent at four-year for-profit schools took out student loans in 2007, compared with about 17 percent attending two-year community colleges and slightly more than 44 percent attending four-year public schools, Harkin said.
The U.S. Education Department proposed regulations July 23, which Harkin supports, to block for-profit education programs from getting federal funds if they can't show enough graduates were repaying their student loans or earned enough to repay them.
Education Secretary Arne Duncan said Friday he would delay issuing the "gainful employment" rule until early next year after receiving 91,000 comments, the most ever on an education issue.
Many for-profit colleges urged students, professors and administrators to send in criticisms of the proposal, The New York Times reported.
Kaplan Inc., DeVry Inc. and the University of Phoenix also made larger-than-usual advertising buys, Inside Higher Ed reported.
Kaplan is owned by The Washington Post Co. Publicly traded DeVry runs DeVry University and seven other colleges. The University of Phoenix is a subsidiary of publicly traded Apollo Group Inc., which also owns and operates four other colleges and online public high schools in Washington, Wisconsin and other states.
2014: The Year in Music [PHOTOS]