This study examined 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 19 K-12 teacher 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". The empirically supported learning trajectory instructional approach describes the scaffolding in an explanatory framework that interweaves descriptive tasks with specific pedagogical strategies toward influencing the transformation of teachers' knowledge for teaching their content with technology--their TPACK.