The authors herein justify the need for e-TPCK, an adaptive e-learning system for teaching in-service teachers how to teach with technology. Outlining the instructional design process involved and the adaptivity feature of e-TPCK, it is explained how the system promotes and measures the development of teachers' Technological Pedagogical Content Knowledge (TPCK). Considering the novel alternative of the system to more traditional professional development approaches, the authors conclude with the argument for employing e-TPCK in real classroom settings in a situated way. [For the complete proceedings, see ED579395.]