This document contains five symposium papers exploring sex differences in cognition. The first paper defines the purposes of the study, i.e., to examine which cognitive performance factors are related to sex differences, and to investigate possible biological, social, and psychological factors affecting developmental sex differences. The second paper reports research results indicating that scores on a physical mathematical reasoning measure are related to spatial ability group and that sex differences in ego development exist. The third paper discusses the research finding that some affective parent behaviors are related to spatial ability groups. The absence of differential parental socialization of boys compared to girls is also discussed. The fourth paper focuses on the lack of evidence that sex-typed activities of the adolescent sample are related to spatial ability groups. The final paper presents the finding that later maturation is related to higher spatial ability and notes that this effect did not appear to operate through brain lateralization. The document concludes with a brief overview of the future research steps. (NRB)