The paper addresses the role of educational task design in implementation research. Its point of departure is the first revision of a task developed for 4th grade in collaboration with a Danish school teacher. The authors informed the task from a hypothetical learning trajectory that requires students to draw on their knowledge both of mathematics and programming and computational thinking. From a task-design standpoint, the teacher's experience proves necessary to adapt the task to local reality. The collaborative process illustrates broader implementation issues, such as problems and roles of different stakeholders, innovation adaptation and capacity building. The lessons are consistent with the emergence of design-based implementation research as a more comprehensive model.