Introduzione alla dimostrazione all'inizio della scuola secondaria superiore

Abstract A research project was carried out with the main objective of studying the possibility of introducing a deductive approach to geometry. The experiment concerns the activities at 9th and 10th grade level (14 - 16 year old pupils). The main point we were interested in concerned the change of the status of justification in geometrical problems. This modification is strictly related to the passage from an 'intuitive' geometry as a collection of facts submitted to empirical verification, to a 'theoretical' geometry, as a system of relations among statements, validated by proof. The experience is centred on the activity of construction, in particular in the Cabri environment; and aims to introduce pupils to the theoretical meaning of justification. The main ideas which constitute the theoretical reference frame are the following. * The theory of figural concepts. * The Cabri-géomètre environment as a "context" for the construction of the meaning of proof. * The collective discussion as a basic element in the social construction of knowledge.