The main aim of this study was to investigate the development of the correlation between family education and student achievement in Sweden, which previous research has found to be stable, in spite of increasing school segregation and widening differences in levels of achievement between schools. Based on register data for populations of graduates from compulsory school between 1988 and 2014, correlations between parental education and student grades were estimated. The correlation was found to increase by 0.04 units between the early-1990s and 2014. The main reasons why this has not been found in previous research are that too coarse a categorization of parental education has been used, a declining quality of measurement of grades, and demographic changes related to immigration.