FRONTLINE/World investigates one of its own stories — "The Play Pump" — an apparently breakthrough idea to harness the energy of children to pump drinking water throughout remote areas of southern Africa. After FRONTLINE/World aired the story in 2005, major donors in the United States — and the U.S. government itself — launched a multimillion-dollar campaign to install the device in thousands of African schools and villages. Now, correspondent Amy Costello investigates what happened to those communities as the promise of the Play Pump fell short and the device's biggest American boosters began to back away from a technology they had once championed.

• Abdul Qadeer Khan