Fluid Intelligence Test Scores Across the Schooling: Evidence of Nonlinear Changes in Girls and Boys

Abstract

The results of the analyses of the changes of fluid intelligence scores measured by the Standard Progressive Matrices test across all school years were presented. Sex differences in fluid intelligence scores for each year of schooling as well as in fluid intelligence changes across schooling were analyzed. A total of 1581 participants (51.1% boys) aged 6.8 to 19.1 years from one public school were involved in this cross-sectional study, of whom 871 were primary schoolchildren (mean age = 9.23; range 6.8–11.6), 507 were secondary schoolchildren (mean age = 14.06; range 10.8–18.0), and 203 were high schoolchildren (mean age = 17.25; range 15.3–19.1). To examine the changes in fluid intelligence both correlation analysis and polynomial regression of the total, boys’ and girls’ samples were performed. Linear, quadratic, and cubic regression models were fitted to the data. To explore sex differences in fluid intelligence in each year of schooling, the series of ANOVA were carried out. The results revealed that the school-age change in fluid intelligence is nonlinear for both girls and boys. The changes for girls during the schooling are best described by a quadratic relationship while those for boys are best reflected by a cubic relationship.