Physics and plasticine.

Abstract

AbstractWe argue that children's failure on one of Jean Piaget's best known tasks, conservation of solid quantity, reflects ignorance of physical properties rather than inadequate reasoning ability. Basing himself on the result of this and similar tests, Piaget claimed that certain sorts of reasoning are not usually possible before certain ages. The educational and, to a lesser extent today, the psychological communities have largely accepted his position. There is opposition but it is mainly addressed to matters of experimental design or problems relating to transition from one stage to the next. We analyze the evidence for conservation itself seen from the child's position. Our paper has implications for the theory of cognitive development but our concerns are largely educational.Children sometimes surprise us both by what they know and by what they do not know. Jean Piaget had a flair for putting his finger on seemingly simple things young children do not know. The upshot of his life's work is a picture of children who live in a strange and chaotic world that is almost incomprehensible to an adult. This does not mean a world free from the cares of rent and income tax, or a world in which ice - cream exercises an almost irresistible fascination. Piaget meant a world whose furniture does not behave in the sober way in which adults expect it to, a world in which the principles of logic and physics have little purchase. We believe that, give or take a few years, Piaget was often right about what children fail to do but wrong about why they fail. We believe further that the impact of Piaget's work was to underrate the intellectual capacities of children. There have, of course, been dissentient voices -- in psychology see, for example, Gelman (1969), Brainerd (1974), Siegel & Hodkin (1981), Siegal (1991); in the education literature Wollman (1982) and Violato (1989). Dissatisfaction has tended to focus on the form of the test question and the presuppositions it generates in children's minds, on the age at which children conserve solid quantity, on the problem of how children pass from one supposed Piagetian stage to another, and other such important matters. Nevertheless, again and again in child development textbooks Piaget's view of children's minds is taken as broadly right. His picture of mental development has been presented to teachers as though it were establishedorthodoxy (e.g., Renner & Lawson, 1973, Lehman, Kahle & Nordland, 1980; Za'rour & Gholan, 1981, Cohen, 1982, Posner, Strike, Hewson, & Gertzog, 1982, Sehman, Krupa, Stone & Jaquette, 1982, Adey, 1987) or as empirical fact (e.g., Bond, 1980, Lawson, 1980). Interested people are told that the main reason for children's failures in scientific understanding is that they have not reached the Piagetian level of maturity at which a particular insight is possible.We believe that Piaget's picture of mental development rests on a much wobblier basis than most people realize. We propose to make our case by concentrating on one of Piaget's best known tasks, conservation of solid quantity. His results reveal something interesting about children, but not at all what he claimed. To show this our main strategy is to examine, from the child's point of view, the evidence that can be adduced for conservation of volume. Piaget's work was, of course, prodigious in scope. We have chosen to concentrate on the conservation task because it is central to his thinking and because it is relevant to our interest in physics education.Piaget and collaborators (see, for example, Piaget & Inhelder, 1941) would present children with a ball of plasticine and ask them to make another ball just as big and as heavy as the first. When the children were satisfied that the two balls had the same amount (la meme chose de pate), the adults took one of the balls, rolled it into a sausage or flattened it into a pancake, and asked: Is there the same amount of plasticine in the sausage or pancake as in the other one? …