Approaching decimal numbers and their operations: the importance of an effective navigation between representations

Abstract

This article deals with aspects and ideas about tasks that can be explored with pupils related to the multiplication of decimal numbers, discussing the mathematics teaching knowledge underlying the preparation and conduction of these tasks. Some of the representations of this multiplication are discussed, as well as the importance of a rich and well-grounded mathematics teaching knowledge to promote meaningful mathematical knowledge for students through an efficient navigation between representations. The choice of representations is also intended here to make explicit the reason why, when multiplying two decimal numbers, the number of decimal places of the product is the sum of those of the factors. The text is based on a collaborative work developed during the last years with teachers of the 1st cycle of basic education (pupils with ages between six and nine), having as its starting point the discussions that took place therein, and the underlying reflections and largest difficulties experienced both by pupils and by their teachers. It should be noted that approaching at the same time the representations of numbers in decimal and fractional forms allows pupils to become aware of different representations for the same value, the same happening when various quantities are used as discrete units, or when different types of units are employed. The teacher has to be in possession of well-founded mathematics teaching knowledge, so as to be able to make use of these distinct representations in a constructive way, and so that they will be meaningful for the pupils.