This paper criticizes Zajonc's confluence model of the relationship between sibling spacing and sibling intelligence. According to Zajonc, variations in the intellectual performance of individuals are accounted for in part by two features of the individual's family of orientation: (1) the number of children in that family, and (2) the spacing between those children in a family. This model is criticized for (1) inconsistencies in the relationship between child spacing and intelligence in the data reported in Zajonc's paper; (2) the failure to present previous child spacing-intelligence data which conflict with the confluence model and (3) the problem of using between-family data for making within-family inferences about intelligence. New within-family data are presented which indicate that there is essentially a zero relationship between child spacing and academic achievement. (Author/BH)