Most studies on the relationship between students' socioeconomic status (SES) and student achievement assume that its effects are sizable and causal. A large variety of theoretical explanations have been proposed. However, the SES-achievement association may reflect, to some extent, the inter-relationships of parents' abilities, SES, children's abilities, and student achievement. The purpose of this study is to quantify the role of SES vis-à-vis child and parents' abilities, and prior achievement. Analyses of a covariance matrix that includes supplementary correlations for fathers and mothers' abilities derived from the literature indicate that more than half of the SES-achievement association can be accounted for by parents' abilities. SES coefficients decline further with the addition of child's abilities. With the addition of prior achievement, the SES coefficients are trivial implying that SES has little or no contemporaneous effects. These findings are not compatible with standard theoretical explanations for SES inequalities in achievement.