WASHINGTON — The United States spent $64,597 to build a wall around a school in Qala Nazir Baba, a village in Logar Province in Afghanistan. It spent an additional $41,792 to rehabilitate an irrigation system in Zoya, a village in Wardak Province.

Both projects were part of a “stabilization” program intended by the United States Agency for International Development to supplement military operations against the Taliban and to demonstrate to Afghans the benefits of supporting the government in Kabul. But according to an internal study evaluating the impact of American assistance in Afghanistan, the result was just the opposite. Villagers believed that the projects would not have been allowed to take place without the Taliban’s approval, and so their support for the Taliban, rather than for the United States or the Afghan government, actually increased because of the aid.

“Worryingly, stabilization programming actually had the perverse effect of increasing support for the Taliban in Taliban-controlled villages,” said the study, carried out for U.S.A.I.D. by Management Systems International, an agency contractor. Qala Nazir Bab and Zoya were among 13 villages where support for the Taliban increased, according to the study, which was released in April.

Senior officials from the aid agency, defending their projects, said the Afghan villages mentioned in the study represented a small proportion of those that have received American assistance.