Shared instructional leadership may support informed decision making on matters of curriculum, instruction, and assessment. Given the various organizational processes and outcomes associated with this construct, it is important to be able to measure the degree to which it exists in schools. In this article we propose the Shared Instructional Leadership Scale and report its reliability and the validity of its factor structure. The scale was designed to assess the extent to which faculty perceive that principals, teachers, and school staff collaborate on instructional leadership practices. Drawing from a sample of 422 teachers nested in 107 schools, we generated four sub-samples to examine its psychometric properties. Next, using exploratory factor analysis techniques, we found the Shared Instructional Leadership Scale factor structure to be stable across all four sub-samples. Finally, we conducted confirmatory factor analysis on a second school-level sample (n = 103) and the results confirmed the Shared Instructional Leadership Scale had a unidimensional structure. We conclude with a discussion of the potential of the Shared Instructional Leadership Scale to inform practice and implications for future research, including directions for further scale validation.