FREUDENTHAL, H. (1978): Weeding and Sowing-Preface to a Science of Mathematical Education, Dordrecht, D.Diedel. HART, K. (1981): Children’s understanding of Mathematics: 11-16. London, J.Murray Lid. NOELTING, G. (1980,a): “ The development of proportional reason- ing and the ratio concept. Part 1: Differentiation of stages”, Educational Studies in Mathematics, 11, 2, 217-253. NOELTING, G. (1980,b): “ The development of proportional reason- ing and the ratio concept. Part 2: Problem-structure et succesive stages; Problem solving strategies and the mechanism of adaptative restructuring”, Educational Studies in Mathematics, 11, 3, 331-363. PIAGET, J. ; INHELDER, B. (1948): La represéntation de l’espace chez l’enfant, Paris, P.U.F PIAGET, J.; INHELDER, B. (1972): De la lógica del niño a la lógica del adolescente, Buenos Aires, Paidós. PIAGET, J.; GARCIA, R. (1971): Les explications cuasales, Paris, P.U.F PIAGET, J.; INHELDER, B. (1974): La gènese de l’idée de hasard chez l’enfant, Paris, P.U.F, 2o ed.
