Computational thinking (CT) is playing an increasingly relevant role within disciplinary teaching in elementary school, particularly in science. However, many teachers are unfamiliar with CT, either because their education occurred before the popularization of CT or because CT instruction was not included in their pre-service coursework. For these teachers, CT professional development (PD) becomes a primary mechanism to close their CT knowledge gap. While CT PD has demonstrated success at increasing teacher's CT understanding, researchers have reported varied outcomes in supporting teachers to write CT-integrated lesson plans. To explore how we might support teachers to integrate CT into elementary science, we employed design-based research (DBR) in a dual-track design of in-class CT instruction for pre-service undergraduates within an elementary science methods class paired with a collaborative, multi-month PD opportunity for pre- and in-service teachers. In this article, we reflect on our 5-year period of DBR and present our design insights and implications for CT instruction and curriculum design from each iteration. Our findings on best practices will inform both teacher educators and PD providers within CT education. Our work will also be of interest to researchers considering DBR for technology-based educational projects.