In this paper we describe and reflect on the design of a mathematical learning activity developed in collaboration between teachers, researchers and technical developers. By making use of augmented reality (AR) as a technology supporting augmentation of a real-world projection with computergene- rated images, we have designed an activity that promotes unique action and learning trajectories. These trajectories require the learners to engage in interactive-constructive actions that involve and stimulate the development of their self-regulatory skills by inviting them to vary and coordinate across the contextual affordances of the technologies and the physical resources in the classroom. Our learning activity is designed as a collaborative guided inquiry, implemented in a regular classroom and involved mathematical problem solving in relation to the geometric concept of scale. In order to successfully complete the activity, the learners are challenged to coordinate affordances from three distinct referential contexts by involving physical and virtual artifacts. In the design process, we identify critical aspects of the activity and embed affordances for corresponding scaffolding actions which turn out to play a crucial role when the activity is implemented with a group of four 15-year-old students. Although the AR technology has served us well in developing this particular activity, this specific technology appears to have limited applicability in mathematics education beyond geometry. We recommend that future research efforts move beyond AR and consider the broader context of embodied design with tangible user interfaces, that have recently shown great potential for the design of innovative activities for the learning of mathematics.