This paper investigates the relationship between activity design and discourse on a mobile learning trail, considering the physical affordances of the real world platform in designing contextual learning experiences. We adopted a context-oriented and process-oriented pedagogical approach in designing the mobile learning trail conducted at Singapore Sentosa Island. Activities were categorized into performative and knowledge-generative on a continuum from well-structured to ill-structured activities. To examine the impact of activity design on discourse types, all audio-recorded verbal data of the three groups of secondary students was analysed with respect to two key dimensions in the knowledge construction process, namely, the epistemic and the social. Analysis showed that activity types and physical affordances of the learning environment have a definitive bearing on group discursive moves. Importantly, the presence of a real world context could generate critical thinking and collaborative knowledge building even for mundane performative activities when they are embedded with unforeseen contextual variables. We argue that the design of activity and the degree of its structuredness, and the assumed desired learning outcomes, are very much subjected to the affordances of physical and social resources in the mobile learning environment-a missing dimension that could possibly be overlooked and understudied.