Background and Context: Integrating computer science (CS) and math in classrooms is an increasingly recognized way for schools to address national CS mandates. There is a need to understand how professional development (PD) can support teachers to integrate. Objective: We examined math teachers' interest, and confidence, in math, CS, and student learning, in relation to their participation in professional development (PD) designed to support them to integrate CS with math in their classrooms. Method: We used mixed-methods to study participants in entry-level hybrid PD, and a sub-group of those participants who took the workshop a second time. Findings: Results showed that not all math teachers have an interest in math, and that math interest significantly influenced whether teachers (a) returned to retake the entry-level workshop and (b) followed through to integrate CS in their teaching. Implications: Findings suggest that workshop design include: (1) multiple points of entry, (2) pairing/grouping participants based on interest and confidence, and (3) opportunities to practice.