In this paper we propose a comprehensive model, conceived as a heuristic to support a co-disciplinary approach to the design, development and analysis of the didactical system, in particular in the case of mathematical e-learning situations. It has been developed by expanding the classical didactical triangle into a tetrahedron, and including within it a mediatory sphere whose intersection points with the tetrahedron can shed some light on the impact of technology within the didactical system. We explain how the model could address the need to take into account, in a co-disciplinary mode, different theoretical and empirical perspectives, within and beyond mathematics education.