Computational Thinking (CT) is a problem-solving process applicable across all disciplines. It has been defined as a 21st-century skill (Wing, "Communications of the ACM," 49(3), 33-35, 2006). Unfortunately, little pedagogical research is available to guide teachers and designers when devising a CT course. This study addresses this issue by describing how a framework to teach CT to second-level students evolved. This framework, ADAPTTER, has been shown to result in a high quality, engaging, low threshold, effective, and practical course. A three-phase Educational Design Research study was employed to develop this framework. It involved six schools, eleven teachers, four content experts, and 446 students. Data was gathered using various means: teacher interviews and diaries, students' questionnaires, artefacts, and tests. The ADAPTTER framework is offered as a way for teachers and researchers to design a CT course, understand its components and have conversations around the same.