Providing college students with free textbooks is no easy task. That seems to be the major lesson from several efforts to produce e-books that are low-cost or free to help reduce students' costs. Money pressures, slow adoption by professors, and quality concerns stand in the way as these projects hope to rival traditional publishing. Take Flat World Knowledge Inc., an upstart publisher that had been a key proponent of a so-called "freemium" model of giving away electronic copies of textbooks and asking students to pay for extras like flash cards or printed copies. The company announced a sudden move away from that model in November, stating that its free-content option will no longer be available starting in January. The reason for the change: Students were not buying as many printed copies as predicted because those who wanted one got a used copy rather than buy a new one from Flat World. Flat World will still offer textbooks at lower prices than traditional publishers do, but nothing will be free. The company's basic online books cost about $20 each. Flat World Knowledge is also pursuing a sponsored-licensing model with some colleges, where an outside company or foundation would enter into an agreement with Flat World Knowledge or the college to help pay for the cost of content. The e-book company will be able to judge the impact of its "free to fair" pricing transition by next year. Some see Flat World Knowledge's move away from the freemium model as a warning for other open-access textbook projects. Finding ways to support the production of free textbooks is not the only unresolved issue for open-textbook proponents. Another challenge is getting buy-in from instructors, who must be persuaded to adopt the textbooks. And when books are written by volunteers, keeping quality high can be more difficult than in the traditional model, where authors are paid by publishers. Producing free textbooks may sound like a good idea, but it is turning out to be easier said than done.