Computational Thinking is a problem-solving process that draws on concepts fundamental to Computer Science. These concepts can support problem-solving across many disciplines. The Digital Strategy for Schools (2015-2020) describes the Irish Government's intention to give every student in compulsory education the opportunity to learn Computational Thinking. This research is an Educational Design Research study underpinned by a pragmatic approach and concerned with Computational Thinking. It aims to answer the following question: what are the characteristics of a practical, engaging, effective, high quality, and low threshold course for both the learning and teaching of Computational Thinking to Irish post-primary teachers and students? This study also aims to validate whether unplugged activities can be successfully used to teach Computational Thinking. This research study had three phases: preliminary analysis, prototype, and semi- summative. It was conducted in six schools with eleven teachers, four content experts, and over four hundred and forty six students. Data was gathered using various means: interviews, focus groups, teacher diaries, students' questionnaires, and students' artefacts. The analytic approach was mixed; it involved content and thematic analysis as well as descriptive statistics. This study found that the following characteristics: activities, demonstration, application, pre-activation, transparency, theory, exemplification, and reflection (ADAPTTER) gave rise to a practical, engaging, effective, high quality, and low threshold Computational Thinking course. This study validated the use of unplugged activities as a pedagogy for teaching Computational Thinking.