In this paper, we present a mathematics teacher’s reflections on the design and experimentation of
an activity sequence involving transitions from ‘pen-and-paper’ mathematical explorations to
mathematical explorations within three different digital environments, GeoGebra, the Scratch
programming environment and Excel. We look at her arguments for supporting students’
development of Mathematical Digital Competency (MDC) and reflect on her instrumental
orchestration approaches. We then argue and discuss the idea of MDC for teaching (MDCT) using
this expert teacher’s case as an exemplar for such practice
