This study investigates the effect of socio-economic level (lower and upper-middle), race (black and white), and sex on locus of control of reinforcement scores, and the relationship between the latter scores and reading achievement in a sample of 211 second grade children. A stratified random sampling technique insured adequate levels of each dependent variable. Administered within a two-month period were: the paragraph meaning and word reading sections of the Primary I and Primary II levels of the 1964 Stanford Achievement Test; four subtests from Cattell's Culture Fair Intelligence Test; and the Bialer-Cromwell Children's Locus of Control Scale. Analysis using a 2x2x2 factorial design found that, among the independent variables, only the main effect of socioeconomic level (SEL) and the interaction of SEL and race effects on locus of control scores were significant. The sole significant relationship between locus of control and reading scores was that white upper-middle SEL subjects having higher external scores had lower reading scores. Intelligence quotient was related to reading, but not to external scores in both SEL groups. The low reliability obtained using the Locus of Control scale indicates need for further development of this scale. (JM)