We have designed, implemented and evaluated a didactical situation where 27 students in grade 4 created large triangular constructions in an outdoor environment by involving a customized GPS-based mobile application. The students’ strategies for construction were reflected upon during a teacher-led discussion involving web technologies and aiming at the formulation of principles for construction. The effective communication of underpinning theories and possible learning objectives, in combination with user-friendly mobile and web technologies, served to scaffold the teacher’s successful orchestration of a logos-oriented mathematical discourse.