Competency-based education (CBE) reform has become a priority in many local and state education agencies in the United States. An oft-cited goal of CBE is to reduce inequities in student achievement outcomes and achievement gaps while improving the overall quality of education. The purpose of this study was to construct a reliable instrument to measure K-12 CBE implementation at the school level. This article describes our instrument development process including construct validation and reliability testing with 413 public school principals. This study employed confirmatory factor analysis and Cronbach’s alpha internal consistency estimates to examine the construct validity and reliability of the pilot administration of the CBE Implementation Survey for Principals. Results suggest that the survey instrument accurately and reliably measures the essential elements of CBE, providing initial support for use in evaluating K-12 CBE implementation. Implications for research, policy, and practice are discussed.