We report the critical case of an expert teacher, with whom we codesigned, implemented and discussed an innovation consisting of a task addressing a dual learning goals that uses block programming in a geometry lesson for her sixth-grade class. We analyse the case focusing on three sub-processes of implementation. First, the teacher constructs agency over both the structure and content of the innovation, illustrated by altering the sequencing within the task and adding of an open-ended activity. Second, her practice changes to adapt the innovation by bringing her expertise in programming and mathematics teaching to guide the solution of one hybrid task. Third, the innovation is adapted to accommodate her pedagogical approach and push for appealing to students’ personal interests. Despite the realisation of these sub-processes, the outcomes of the realised innovation were not necessarily positive, implying a need for an integrated — not compound — expertise in computational and mathematics teaching.