Lindleigh Whetstone wears headphones as she shoves clothes into the washing machine. Her classmate, Stepheno Zollos, wears them as he shops for groceries. An onlooker might assume the teens are listening to the latest top 40 hit, but they’re really learning Spanish.

Whetstone and Zollos are students in Kathy O’Connor’s class at Tidewater Community College in Virginia. O’Connor got an $11,000 grant from the school to lend her students iPods so they can practice their Spanish conversations anywhere–not just sitting in front of a computer.

“I get a lot more listening in than I did before,” said Whetstone, who estimates that it’s increased from about 30 minutes a week to four or five hours.

Students are using MP3 players more frequently to listen to downloaded books, study guides, and language labs on the go. The percentages are still small, according to a recent study by market research firm Harrison Group that surveyed 1,000 teens in September. Music listening made up about 85 percent of MP3 use among teens, video was about 10 percent, and podcasts and audio texts fell under the remaining 5 percent.

But the actual numbers are growing, and companies that make educational materials are banking on them climbing higher.

Over half of teens owned a portable MP3 player in mid-2006, according to a study of digital music behavior conducted by market research firm Ipsos.

“Students are more mobile today. Their expectations of being able to get digital content is certainly much higher than it has been in the past,” said Scott Criswell, product manager of online delivery systems for the higher-education unit of McGraw-Hill, one of the three biggest textbook publishers. Criswell said the company now offers more than 800 digital products, most with audio, and that figure has increased by 50 percent over the past four years.

Teachers, especially at the college level, are increasingly making resources available in MP3 form: Michael Barrett, a cardiologist at Temple University, even put recordings of heart murmurs online so his medical students could download and listen to them, instead of squeezing in time with a patient. “The iPod becomes a simulated patient, really,” Barrett said.

In response, new products have been popping up.

Audible, the biggest audio book seller, and Pearson Education, the biggest textbook publisher, teamed up last summer to launch VangoNotes, textbook chapter summaries and reviews in MP3 form. The companies said thousands of students have downloaded the more than 100 titles, which should grow to 200 titles by this fall.

“Right now it’s a small part of our business, but we believe it’s going to be a growing part of our overall strategy,” said Sandi Kirshner, chief marketing officer of Pearson’s higher-education unit.

It’s not just college students; grade schoolers are starting to do their reading with earphones, too.

One type of audio player called Playaway–a two-ounce Flash player pre-loaded with an audio book made by Follett and Findaway World–was sold to school districts starting about six months ago. The players are now on loan at roughly 1,500 libraries, 15 percent of which are school libraries.

Belinda Jacks, who oversees 38 school libraries in the Dallas suburb of Grand Prairie, recently ordered Playaways for her libraries and said they’ve become “shockingly” popular.

She added that, contrary to some parents’ concerns, listening to books encourages reading. This expands on reading out loud to kids, which studies show boosts literacy, Jacks said.

When you compare traditional books to audio books, however, there’s a big difference in price. A new paperback copy of Charlotte’s Web costs $8 on Amazon, whereas the Playaway version costs $30, and an iTunes download of it costs $17. And that doesn’t even count the cost of an MP3 player for students who don’t have them.

The key is getting schools to help out with the costs, said Tidewater’s O’Connor. Of the 16 students in her class this semester, only two had their own MP3 players at the outset. Marketing experts say the audio book industry is already one of the fastest-growing parts of publishing. And given new technologies that will merge phones and internet browsers with MP3 players, the market could grow even more quickly, said Harrison Group Vice Chairman Jim Taylor.