NEW YORK (MainStreet)—National 529 Day raises awareness about saving for college. But what if college is right around the corner and the pot isn't full? Those who haven't saved enough, or who may want to use their money for something else, perhaps graduate school, may be relieved to know that there is a little-known way to cut the cost of a college degree significantly, in some cases by as much as half: testing out of courses.

Also see: Best College Deals: In State, Out of State and Beyond

Typically, students think of AP exams as a way of earning college credit without going to class. However, these exams require students to have taken high school AP courses.

But there are other knowledge-assessment vehicles by which the college-bound, whether in high school or already in the workforce, can earn up to two years' worth of college credit.

Katherine Avery, a pianist and private music teacher, received 78 credit hours between taking CLEP and DSST exams, plus nine credit hours from taking Excelsior College exams. She also got four credits for a life experience portfolio, plus three credits for learning how the portfolio should be made.

Also see: Does College Add Up? Try This Formula

The College Board offers 33 90-minute introductory-level, knowledge-based College-Level Examination Program (CLEP) exams worth three to 12 credits. Each costs $80 compared to $750, the average cost of a college course. You'll also save on room, board, fees and other costs.

Participating schools determine for which exams they will award credit, how many, and the minimum qualifying score, says Suzanne McGurk, senior manager of the CLEP and Accuplacer programs at the College Board.

The 38 DSST exams by Prometric cover both upper-and lower-level college courses. They also cost $80 per exam. According to its website, there is little overlap with CLEP exam subject matter.

While these two exams essentially test book smarts, the LearningCounts portfolio program helps students use life experience to get college credit. The cost is either $129 for the do-it-yourself program or $500 for an instructor-led course (and three credit hours) on how to put together your portfolio. Each portfolio can earn up to 12 undergraduate credit hours. However, whereas CLEP exams and DSST exams are accepted at thousands of colleges and universities, prior learning assessments (PLA) are only accepted at hundreds of schools.

Excelsior College offers two other exams for college-level credit, which is accepted in hundreds of schools. Each one costs $95.

Some states will pay for high school students to take college-level courses.

--S. Z. Berg is the author of College on the Cheap.

Also see: College Sticker-Shock Strategies: A Father's Odyssey