This paper describes aspects of 13 year-olds activity in mathematics as emerged during the implementation of proportional geometric tasks in the classroom. Pupils were working in pairs using a piece of software specially designed for multiple representation (symbolic and graphical) of the variation in parametric procedures with dynamic manipulation of variable. In this paper we discuss children's use of normalising, an activity in which children "correct" the geometrical figures while developing meanings for ratio and proportion. We discuss the potential of normalising for the construction of mathematical meanings in relation to particular aspects of the pedagogical setting including pupil's interaction within the computational environment as well as task design. [For complete proceedings, see ED489597.]