Joshua Edwards's eighth-grade paper about the Black Plague came with a McDouble and fries.

Joshua sometimes does his homework at a McDonald's MCD +0.55%restaurant—not because he is drawn by the burgers, but because the fast-food chain is one of the few places in this southern Alabama city of 4,000 where he can get online access free once the public library closes.

Cheap smartphones and tablets have put Web-ready technology into more hands than ever. But the price of Internet connectivity hasn't come down nearly as quickly. And in many rural areas, high-speed Internet through traditional phone lines simply isn't available at any price. The result is a divide between families that have broadband constantly available on their home computers and phones, and those that have to plan their days around visits to free sources of Internet access.

That divide is becoming a bigger problem now that a fast Internet connection has evolved into an essential tool for completing many assignments at public schools. Federal regulators identified the gap in home Internet access as a key challenge for education in a report in 2010. Access to the Web has expanded since then, but roughly a third of households with income of less than $30,000 a year and teens living at home still don't have broadband access there, according to the Pew Research Center.

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