In this article we operationalize the Technological Pedagogical And Content Knowledge (TPACK) model as an analytic lens to trace progression in teaching practice. We explore teacher development by studying didactical designs. Didactical design refers to the design of teaching sequences within a particular subject, and includes a pre-planned sequence of lessons, with a detailed teaching plan of how to implement the task in the classrooms. We report from a three-year school development project which involved 48 teachers and over 1000 students in elementary school. An in-depth analysis of 14 didactical designs in the subject of mathematics respectively 13 didactical designs in mother tongue was conducted. The analysis was based on classroom observations, video recordings, chat logs, online forums, interviews and participation in teachers’ daily work. Our position is that our approach can serve as an effective way to categorize, analyze and evaluate didactical designs. © The authors, 2016