This study was conducted to confirm the validity and reliability of the 64-item Measure of School Capacity for Improvement (MSCI). The MSCI was designed to assess the degree to which schools possess the potential to become high performing learning communities, and was developed in response to a paucity of definition, operationalization, and assessment of school capacity in the education research and evaluation literature. The MSCI offers an operationalization of the concept of school capacity. The MSCI was administered to 1,274 professional staff affiliated with 12 elementary, 10 middle, and 13 high schools in Tennessee that were low performing, predominantly African American, and low SES. Results of factor analysis and estimates of internal consistency suggest that the MSCI and 58 of the original items, which comprise six subscales, are very reliable and has construct validity. Moreover, the MSCI holds some promise for providing a much-needed means for discerning schools with the resources, practices, and proclivities to successfully undertake serious development from those who might better focus their energies on first addressing the issues measured by the various MSCI subscales.