The purpose of this article is to explore students' and teachers' perceptions of affordances, and their actualization while interacting with the e-assessment system Numbas and its effect in terms of formative feedback delivery. The article uses affordance theory and a qualitative research design approach to analyze data using semi-structured interviews. Eight interviews were conducted with six students and two teachers. The results reveal the actualization of several affordances such as ease of use and navigation, variation in mathematical contents, congruence to textbook mathematics, support for pen and paper skills, learner autonomy and motivation to engage in mathematical problem-solving. Conclusions and future work based on comparative studies are drawn from the results to promote Numbas formative feedback for teaching and learning mathematics. [For the full proceedings, see ED621108.]