Complementing different software environments to mediate the introduction of variable, parameter and unknown

Understanding, in algebraic expressions and relations, the different roles of letters as variables, parameters and unknowns is hard for students both when building formulae and when interpreting them; nevertheless it is crucial, since these two activities are the base of algebraic modelling. We suggest to lead students to a correct understanding of these concepts by introducing them gradually, through problem solving, complementing different software environments.