Cohort differences in intelligence test performance: effects of primary school education and task difficulty

The results of an analysis of cohort differences in performance on the “Standard Progressive Matrices” test over one decade are presented. The focus of the research is on the performance of the fluid intelligence test by 1008 schoolchildren of six birth cohorts who entered the first grades of one school from 2011 to 2017, and their results after 4 years of primary schooling — from 2015 to 2021. The follow-up study solves problems related to determining the nature of cohort differences in test scores “within” one decade in the first and fourth years of education, the likelihood of changes in the size of cohort differences during primary schooling, and the degree of their dependence on the complexity of test items. The results of the analysis indicate the existence of cohort differences in the performance of students of one general education organization on an intelligence test “within” one decade. At the same time, the nature of the changes does not correspond to the trend of a progressive increase in test scores from the previous cohort to the subsequent one. The magnitude of cohort differences in the first and fourth years of study varies depending on the complexity of test items, reaching maximum values for more complex items. Four years of primary schooling significantly reduces the severity of cohort differences both in the overall score of the “Standard Progressive Matrices” test and in individual series of test items associated with individual thought processes. At the same time, the complexity of test tasks is associated with the influence of primary school education on the severity of cohort differences: the more complex the tasks, the less the magnitude of cohort differences is reduced by the end of primary school.