This paper presents a case study on students' covariational reasoning, that used the
software Function Studium to perform activities about the rate of change of linear and quadratic
functions. Such software was designed by the research group (anonymous) and its development was
guided by a model of software process based on Informatic-Didactic Engineering (anonymous). The
results of the case study pointed out the contribution of activities designed within the software to
support students' covariational reasoning, such as the dynamic and simultaneous connection of the
different notations in the software and the tool "rate of change", which allowed students to infer
patterns of variation of the functions addressed and the transition from average rate of change to
instantaneous rate of change.