Many reforms in past decades have come and gone without having the desired impact on teaching practices. Two shared ideals that reforms have had are offering challenging content by using whole tasks and tailoring student guidance to what students need for effective learning. In this article, we aim to bridge the reform-practice gap by taking a practicality perspective on how reform ideals are presented by exploring the concept of modularity. In this study modularity refers to how teachers can rearrange and adapt lesson-building blocks (e.g. explanation, checking homework or using a whole task) to change their teaching practices in line with reform ideals. We performed an explorative study (school-based PD programme) in which participants designed, enacted and reflected on authentic lessons using their student learning outcomes as input for subsequent lesson designs. Data were gathered about the use of building blocks and how teaching practices were developed in terms of using whole tasks and tailoring student guidance. Results show that participants made ongoing stepwise changes by building on what they already did successfully for both using whole tasks (e.g. change a task to recall into a whole task and shifting it to the lesson start) and tailoring student guidance.