With the increasing emphasis on infusing computational thinking (CT) in PK-12 education, developing teachers' technological pedagogical content knowledge is essential for CT integration. In a graduate online CT course for elementary science, technology, engineering, and mathematics (STEM) teaching, the Authentic Integrated Online Assessment model (Galanti et al., 2021b) informed the design of a digital interactive notebook (DINb) as a performance-based assessment of teachers' CT content and pedagogical content knowledge. Qualitative content analysis of course artifacts revealed the power of the DINb to prompt feedback, revision, and self-reflection. The iterative nature of the DINb deepened CT understandings, normalized incomplete thinking as productive, and enhanced online teacher-instructor communication about CT concepts. Findings indicate that this iterative approach to online assessment developed elementary STEM teachers' CT skills and dispositions. They demonstrated their understanding of CT as a problem-solving approach that they could learn and integrate in their own classrooms.