A crucial step in improving the use of digital technology (DT) for learning mathematical concepts in the classroom appears to be increasing teacher involvement in task development. Hence, this research considered the effect of a professional development (PD) programme designed to assist teachers with DT task production for implementation in their classrooms. Four groups of three Sri Lankan teachers were observed and guided as they designed and implemented DT tasks. We examine the effectiveness of the PD programme in terms of the richness of the tasks produced by the groups before and after the PD. The results suggest the intervention led to richer, more student-centred tasks. The reasons behind this improvement are analysed, along with factors that might have influenced the DT task development. The findings have implications for the design of secondary school PD programmes and may help educators to facilitate the training of mathematics teachers in the use of DT.