Cognitive developmental research has documented that children acquire rich knowledge about the physical and psychological world before they are exposed to science, and that learning science requires substantial ontological, epistemological and representational changes to happen in the conceptual system of the child. For example, Vosniadou & Skopeliti (2005) showed that while the majority of third grade children categorized the earth as a physical object distinct from solar objects like the sun and the moon, 90% percent of 5th graders categorized the earth as an astronomical object, belonging to the same category as the sun and the moon. In the present research we will present two novel, chronometric, tasks for assessing the conceptual re-organizations that take place as children are exposed to systematic science instruction and for further exploring the question of whether naive theories are overwritten or survive and continue to exist together with the scientific theories. References Vosniadou, S., & Skopeliti, I. (2005). Developmental Shifts in Children’s Categorizations of the Earth. In B. G. Bara, L. Barsalou, & M. Bucciarelli (Eds.), Proceedings of the XXVII Annual Conference of the Cognitive Science Society, Italy, 2325-2330.