WASHINGTON (AP) — Worried your kids spend too much time with their faces buried in a computer screen? Their schoolwork may soon depend on it.

Education Secretary Arne Duncan called Tuesday for the nation to move as fast as possible away from printed textbooks and toward digital ones. "Over the next few years, textbooks should be obsolete," he declared.

It's not just a matter of keeping up with the times, Duncan said in remarks to the National Press Club. It's about keeping up with other countries whose students are leaving their American counterparts in the dust.

South Korea, which consistently outperforms the U.S. when it comes to educational outcomes, is moving far faster than the U.S. in adopting digital learning environments. One of the most wired countries in the world, South Korea has set a goal to go fully digital with its textbooks by 2015.

"The world is changing," Duncan said. "This has to be where we go as a country."

The transition to digital involves much more than scanning books and uploading them to computers, tablet devices or e-readers. Proponents describe a comprehensive shift to immersive, online learning experiences that engage students in a way a textbook never could.

A student studying algebra might click to watch a video clip explaining a new concept or property. If they get stuck, interactive help features could figure out the problem. Personalized quizzes ensure they're not missing anything — and if they are, bring them up to speed before they move on to the next lesson. Social networking allows students to interact with teachers and each other even when school isn't in session.

Using digital textbooks, schools can save money on hard copies and get updated material to students more quickly. School districts may also be able to pick and choose their curriculum buffet-style. A district might choose one publisher's top-notch chapter on Shakespeare, but follow it with another publisher's section on Nathaniel Hawthorne's "The Scarlet Letter."

But adopting digital textbooks isn't as easy as a directive from Washington. States set their own processes for selecting and purchasing textbooks that match their needs.

Over the last two years, at least 22 states have taken major strides toward digital textbooks, said Douglas Levin, executive director of the State Educational Technology Directors Association. Until recently, Levin said, states struggled to collaborate because each had its own curricular standards, a particular burden for smaller states. That burden has been eased now that 48 states and the District of Columbia have adopted the Common Core standards, a set of uniform benchmarks for math and reading.

"There are opportunities for the federal government to encourage states and districts not to reinvent the wheel," Levin said.

A school district in Huntsville, Ala., launched an effort over the summer to become the first district to transition fully to digital textbooks. To do that, the district must first ensure every student has either a laptop or a tablet computer. In California, Gov. Jerry Brown signed a pair of bills in September aiming to make his state a national leader in electronic college textbooks.

Still, many districts, already buckling from diminished budgets, don't have the bandwidth or the equipment to make digital materials available to every student. That's created a new challenge for the educational publishing industry as it works to market products to district across the technological spectrum.

"We haven't produced anything that's print-only in over three years. One hundred percent of what we have is available to school districts electronically," said Vineet Madan, senior vice president of new ventures for McGraw-Hill Education.

A central tension in the movement toward digital materials is what it means for textbook publishers whose profits rely on replacing old, worn-out textbooks with new ones. Yet to be seen is whether textbooks, like music, will become easy to steal or copy without payment, or whether the industry will find new ways to make money off of teaching materials.