The design of innovative learning activities supported by mobile technologies calls for the coordination of theories and methodologies from several research domains. The authors of this paper have been engaged in several collaborative research efforts involving expertise in mathematics education and technology–enhanced learning as well as in–service mathematics teachers. Within the methodological framework of design research, we coordinate and make use of specific theoretical and methodological constructs in order to stimulate the collaborative creation of innovative trajectories for the learning of mathematics. We illustrate this design approach by accounting for a specific activity designed to support a learning progression over time and across contexts, aiming at enacting the learning of geometry in an outdoors context. The outcomes of these efforts have provided us with valuable insights into how collaborative design research and mobile technologies can be used in school contexts to guide and support novel ways to enact mathematical learning.