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We investigate the hypothesis that Executive Functions(EFs) are implicated in the learning of science andmathematics by examining the relation betweenperformance in two Science and Mathematics ConceptualUnderstanding and Conceptual Change (CU&C) tasks,and two Stroop-like Inhibition and Shifting EF tasks, in agroup of 69 4th and 6th grader children. The results showedhigh correlations between accuracy performance in theCU&C and EF tasks even when Intelligence Ability (IA)and Age were partialed out. A path analytic model showedthat performance in the CU&C tasks could be explainedby performance in the EF and IA tasks, which werepositively related to each other. Further analyses showedthat accuracy of performance particularly in the CU&Ctasks could be predicted by performance in the EF tasks,with high or medium EF scores being a prerequisite forplacement in the group of high CU&C achievers.

We argue that the acquisition of chemistry expertise requires considerable conceptual changes, which among otherthings involve a change from reliance on visual-spatial thinking to the employment of analytic strategies. We also argue thatthis shift in chemistry and specifically in knowledge about molecular structure is related to the acquisition of expertise and notto individual differences in visual-spatial thinking. In this presentation we will present an experiment designed to investigatethe visual-analytic shift in knowledge about molecular structure in 132 11th graders. The results showed that the students,who were novices in chemistry, could solve the items requiring visual strategies but not those requiring analytic strategies,suggesting that they had not achieved the visual/analytic shift. Additional studies are needed to compare novices and experts inorder to further test our hypothesis regarding the visual-analytic shift in chemistry.

The purpose of this study is to propose a process model to explain elementary school students' solutions of three simple problems in elementary mechanics. Forty eight 5th grade students were given three drawings depicting objects of various sizes in different kinetic states or being pushed by a human agent. They were asked to say whether a force was being exerted on the objects and to explain why. A process model has been proposed to explain students' answers to the three questions. The innovation of the process model is that it attempts to link two levels of representation: A semantic level, where a concept is analysed in terms of the presuppositions, beliefs, and mental models that underlie it and a syntactic level that specifies how concepts are related to other concepts in hierarchical categories. The work has been validated by a computer model designed by the AI team (Vosniadou, Kayser, Champesme, loannides & Dimitrakopoulou, in press).

First, third, and fifth grade children were askedquestions about the shape of the earth and about theday/night cycle. The majority of the children used asmall number of well-defined mental models of theearth, the sun, and the m o o n to explain the day/nightcycle. T h e younger children formed initial mentalmodels which explained the day/night cycle in termsof everyday experience (e.g., the sun goes d o w n behindthe mountains; clouds cover up the sun). T h e olderchildren constructed synthetic mental models (e.g., thesun and m o o n revolve around the stationary earthevery 24 hours; the earth rotates in an "up/down"direction with the sun and m o o n fixed at oppositesides) which are attempts to synthesize aspects of thescientific view with aspects of their initial models. Afew of the older children appeared to have constmcted amental model of the day/night cycle similar to thescientific one. The children's models of the shape ofthe earth provided strong "second-order" constraints ontheir models of the day/night cycle (e.g., children withflat earth models do not explain the day/night cycle interms of the m o v e m e n t of the earth). The changes inthe children's models with age was explained in termsof the gradual reinterpretation of a set ofpresuppositions, s o m e of which are present early inthe child's life, and others which emerge later out ofpreviously acquired knowledge.

argue that children construct a naive understanding of the world which gradually becomes modified to conform to adult-scientific views. This naive understanding consists of a number of discrete ontological beliefs, such as that the ground is flat, that things fall down, and that stars are small objects. Children are capable of synthesizing their ontological beliefs to form relatively consistent conceptual structures. However, they also seem to be operating under an epistemological constraint according to which these ontological beliefs represent the true state of affairs about the world. In the process of conceptual change children replace their ontological beliefs with a different explanatory framework.