Impact on Infection Intensity: Deworming reduced moderate to heavy helminth infections by at least 31 percentage points (76 percent) amongst children in the treatment groups. Pupils that received treatment reported being sick less often, and they had significantly better height-for-age—a measure of nutritional status. Health education had minimal impact on worm prevention behaviors, including observed pupil cleanliness, the proportion of pupils wearing shoes, or self-reported exposure to fresh water. Therefore, to the extent that the program improved health, it almost certainly did so through the effect of the medicines rather than through health education.
Impact on School Attendance and Test Scores: Among girls younger than thirteen years old and all boys who were treated, school participation in the first year after medical treatment increased by at least 9.3 percentage points relative to the comparison group. No improvements in test scores were found as a result of the deworming.
Treatment Spillover: Those living up to 3 kilometers away from treatment schools benefited from “spillovers” of the deworming treatment1, including reduced worm infections and increased school attendance. Spillover effects occur because medical treatment reduces the transmission of infections to other community members. It is estimated that moderate-to-heavy helminth infections among children living up to 3 kilometers away from treatment schools were 10.2 percentage points lower on average, while school participation was 2.7 percentage points higher on average. Including these spillover benefits up to 3 kilometers away, deworming increased school participation by 8.5 percentage points, which is a one-third reduction in school absenteeism.
Cost-Effectiveness: Including the spillover benefits of treatment, the cost per additional year of school participation was US$2.92, making deworming considerably more cost-effective than alternative methods of increasing school participation, such as school subsidies.
1 Worm infections are reduced among schoolchildren living within 3 km of treated individuals, but not much beyond that, although the original paper estimated benefits out to a distance of 6 km due to a coding error. For more on the updated results, see Hicks et al. (2014a), Hicks et al (2014b), and Hicks et al (2015), all cited below. For an update (July 2015) from the authors on deworming impacts on education, see here.