Past research has shown that schooling has a significant impact on individuals' categorical abilities; however, little is known about the effect of preschool attendance on these abilities. The purpose of this study was to explore the impact of preschool education on Turkish children's categorical preferences and categorical achievement. In the study, in order to investigate the short and long-term effects of preschool attendance, primary school children were included in the sample as well as preschoolers. Thus, the sample consisted of 200 children from three different age groups (five-year-olds, first and third grade). Half of the children attended preschool (preschool group), half did not (non-preschool group). Data were collected through individual interviews. As data collection tools, conflict and non-conflict triads were used. Conflict triads were utilised to determine children's categorical preferences, while non-conflict triads were used to evaluate children's categorical achievement. Children were asked to indicate which option was in the same category with the target. Findings showed that there was a significant difference between preschool and non-preschool groups in categorical preferences. Preschool attendance also had a significant effect on children's categorical achievement.