Moderating effects of personality on the genetic and environmental influences of school grades helps to explain sex differences in scholastic achievement

Girls consistently achieve higher grades than boys despite scoring lower on major standardized tests and not having higher IQs. Sex differences in non-cognitive variables such as personality might help to account for sex differences in grades. Utilizing a large sample of 17 year-old twins participating in the Minnesota Twin Family Study (MTFS), we examined the roles of Achievement Striving, Self-Control, and Aggression on sex differences in grade point average (GPA). Each personality trait was a significant predictor of GPA, with sex differences in Aggression accounting for one-half the sex difference in GPA and genetic variance accounting for most of the overlap between personality and GPA. Achievement Striving and Self-Control moderated the genetic and environmental influences on GPA. Specifically, for girls but not boys, higher Achievement Striving and Self-Control were associated with less variability in GPA and greater genetic and environmental overlap with GPA. For girls, certain personality traits operate to shape a context yielding uniformly higher GPA, a process that seems absent in boys.