In contrast to earlier in the HIV/AIDS pandemic, net of other demographic factors, formal education acts as a preventative factor in sub-Saharan Africa. Despite this trend, there has been almost no research on the causal mechanisms behind the widely reported education effect. Consistent with the education effect, structural equation modeling of the influence of education attainment on condom use with Demographic Health Survey data from nine sub-Saharan Africa nations collected between 2003 and 2005 finds that net of control variables, there is a robust, positive influence of education on condom use among sexually risky adults. Information-transfer and attitude change, the two most commonly assumed educational influences on the use of condoms, are tested, and although education attainment increases acquisition of basic facts and the inculcation of positive attitudes about HIV/AIDS, these factors have only weak influence on condom use. Given this, a new hypothesis about education’s enhancement of health reasoning is developed from neuro-developmental and decision-making research. Modeling finds that education robustly influences health reasoning ability and this factor mediates a significant proportion of the education effect on condom use. The results raise concern about the enormous effort by NGOs in the region to use mainly fact- and attitude-based educational programs to reduce future HIV infections. Future research on the causal mechanisms behind the association between education and HIV/AIDS prevention should focus how on schooling enhances the cognitive skills needed for health reasoning.