“…For investigating development of human conceptions, several models have been proposed, both in Cognitive Sciences (e.g., VanLehn, 1990VanLehn, , 1993diSessa, 1993diSessa, , 1996Tiberghien, 1989;Vosniadou, 1995;Chi, Slotta, & de Leeuw, 1994;Anderson, 1985;Simon, Newell, & Klahr, 1991) and in Artificial Intelligence [Klahr & Siegler, 1978;Sage & Langley, 1983;Forbus, & Gentner, 1986;Laird, 1983;Rumelhart, 1989;Newell, 1990;Sleeman et al, 1990;Pazzani, 1991;Shultz, Mareschal, & Schmidt, 1994;Baffes & Mooney, 1996;Schmidt & Ling, 1996]. However, most computational models of human learning, even though interesting under many respects, are based on excessively simplifying assumptions, especially for what concerns representation of knowledge, which is often reduced to a set of simple "Condition → Action" rules.…”