This study contributes insights into how task design with different elements of guidance may influence students' utilization of dynamic software for problem solving and reasoning. It compared students' solving of two tasks with different designs supported by the dynamic software GeoGebra. Data analysed examined students' approaches to utilizing GeoGebra, the characteristics of their reasoning and their ability to prove the validity of their solutions after solving the problems. The results showed that students who solved the task with less guidance (without instructions about a specific solving method) were better able to utilize GeoGebra's potential to support their reasoning and problem solving. These students reasoned more creatively and presented more advanced proofs for their solutions than the more guided ones. Keywords GeoGebra. Creative reasoning. Task design. Non-routine tasks A recurrent question in educational research is whether and how technology may support students' learning mathematics. Dynamic software, in this case GeoGebra, invites students to create and manipulate geometric and algebraic representationsfeatures that are considered to have the potential to support problem solving and reasoning (Falcade et al. 2007; Preiner 2008). In situations where students make use of these potentials, they create mathematical objects based on questions or hypotheses. They then interpret, assess and transform the outcomes to proceed in their problem solving. The results, however, are assumed to come from the students' engaging in problem solving and reasoning, and their use of the features of the software to do so. However, it is important to know, rather than simply to assume, what students do when they use dynamic software such as GeoGebra and what guides them in using the