This study sought to identify factors that affect teachers' beliefs about teaching computing in their classrooms. By reviewing existing scales and research on computing, we created the Teacher Beliefs about Coding and Computational Thinking (TBaCCT) scale. Through confirmatory factor analysis and structural equation modeling we validated the scale with data from 245 elementary teachers from eight U.S. school districts who participated in computing teacher development and taught coding to elementary students over one school year. Teachers' self-efficacy for coding and computational thinking increased significantly as they taught coding, while their teaching efficacy for computing increased the most. The resulting 33-item TBaCCT provides a validated scale that can be used to measure elementary teacher beliefs about computing education as they engage in teacher professional development.