This study explored the influence of a researcher-conjectured learning trajectory instructional approach toward the enhancement of teachers’ technological pedagogical content knowledge (TPACK). The study provides a rich description of how a learning trajectory, situated within a social metacognitive - constructivist instructional framework, influenced the participants’ thinking about their own thinking with the technology in learning mathematics/science and their thinking about their students’ thinking and understanding when learning with the technology. Three themes emerged: The learning trajectory as an ordered network of experiences is multi-faceted; the tools are used for sharing knowledge as well as constructing knowledge; and the tasks sequence the participant in the role of a ‘teacher as a student’ transitioning to the role of ‘teacher as a teacher’.