E-assessment systems such as Numbas are now widespread in mathematics education at the primary, secondary, and tertiary level. However, little is known about the affordances and constraints of Numbas in mathematics teacher education. The purpose of this study is to investigate the emergence, perception, and actualisation of Numbas affordances and constraints, and their effect on teaching and learning mathematics. The study draws on Gibson's affordance theory and associated research in the field of digital technology. It follows a qualitative research design to generate data using semi-structured interviews of six students and two teachers. Data from the interviews were analysed thematically to highlight the affordances and constraints of Numbas and their effect on mathematical learning and teaching. Future work will continue exploring Numbas affordances and constraints for learning and teaching mathematics in similar educational settings to ensure more validity and reliability of the results.