The rapid expansion of computer science (CS) instruction in primary and secondary education has highlighted the shortage of teachers qualified to teach the subject. A key strategy for building CS teaching capacity has been preparing teachers of other subjects (e.g., math, technology applications, business) to teach introductory CS through short-term professional development (PD) workshops, online training modules, micro-credentials, and teacher meetups or conferences (Christensen Institute, 2019). As various new CS curricula and activities using different computational representations or programming environments are rolled out each year, it can be difficult for teachers to make sense of how they map to CS standards or fit with existing activities. To benefit a wide range of teachers using a variety of CS curricula across different programming languages, CS teacher PD needs to focus on CS standards and CS content and pedagogical knowledge rather than merely the details of a particular curriculum. This white paper details the elements of effective CS education, known teacher challenges in CS education, and the current state of CS teacher PD. It also describes an approach to address some of these teacher challenges and help teachers understand CS standards and develop their CS formative assessment skills. The white paper concludes with recommendations for CS teacher PD design and suggest actions for states and school districts to support CS teachers.