Data from 723 families tested for ocular refraction, measures of cognitive ability and school achievement, and measures of school-related nearwork activity were analysed, to examine the association of nearwork and intellectual ability with the development of myopia. The basis of the tests was detection of heterogeneity of standardized regression coefficients, derived from the regression of spherical refraction on age, between scaled nearwork or achievement measures. The results did not provide any evidence in support of the hypothesis that nearwork influences myopia but did confirm a relationship between school grades and myopia.