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.