The importance of developing individuals' computational thinking (CT) skills has given rise to many practices and research and development initiatives. Although there is a considerable volume of research on improving students' CT skills, remarkably little is known about teachers' design work to improve students' CT skills. This multiple case study aimed to explore high school computer science teachers' instructional design (ID) process. Data were collected through interviews, lesson plans, and classroom observations from three K-12 cases. The results showed that teachers' ID processes had both similarities; including the design steps, the analysis step predominance, and the interaction intensity between the stages, and differences; included the number of interactions and the connections within the stages. Moreover, teachers' beliefs about teaching and learning CT affected ID process.