Doing long sums in the absence of complementary actions or artefacts is a multi-step procedure that quickly taxes working memory; congesting the phonological loop further handicaps performance. In the experiment reported here, participants completed long sums either with hands down—the low interactivity condition—or by moving numbered tokens—the high interactivity condition—while they repeated ‘the’ continuously, loading the phonological loop, or not. As expected, articulatory suppression substantially affected performance, but more so in the low interactivity condition. Independent measures of basic arithmetic skill and mathematics anxiety moderated the impact of articulatory suppression on performance in the low but not in the high interactivity condition. These findings suggest that working memory resources are augmented with interactivity, underscoring the importance of characterizing the properties of the system as it is configured by the dynamic agent-environment coupling.