Data are presented from families of monozygotic twin pairs which give evidence of genetic variance on the Block Design Test, a nonverbal measure of intelligence. Analyses of genetic and environmental effects on behavior are possible with this kind of information. (SA)

Results of seventh-grade students taking Scholastic Aptitude Test indicate that, by age 13, a large sex difference in mathematical reasoning ability exists; among students scoring greater than 700, boys outnumbered girls 13 to 1. Hypothesized factors thought to influence the difference (such as course taking, attitudes) were not supported by data…