Using a fairly rich data set from South Africa, the paper finds that, despite the sobriquet `gutter education', the African schooling systems help to create cognitive skills, and these skills are a determinant of wage levels. Various robust estimators are used but the influential outlier problem does not turn out to be serious. Computational skills appear to be more important than comprehension skills in influencing wages. The African primary schooling system was an extremely poor generator of computational skill, the seven-year course raising the computational test score by 13%, if that. A policy implication is that productivity could be raised by certain near-costless reallocations of resources in favour of mathematical learning.