In this article, we explore how students' agency relates to both highly structured and open-ended learning environments. This is done by analysing how students' understanding of tasks evolves through their activities in relation to the representations inscribed in two technology-rich learning environments. Based on the sociocultural approach to thinking, reasoning and learning we argue that it is necessary to include activities, artefacts and aspects of the knowledge domain in order to understand how and what the students' learn. We conclude by arguing that the process of understanding a task is often complex and ongoing through the activity.