The purpose of the mixed methods study was to develop and validate the CSIS-360, a 360-degree feedback assessment to measure competencies of school improvement specialists from multiple perspectives. The study consisted of eight practicing school improvement specialists from a variety of settings. The specialists nominated 23 constituents to provide 360-degree feedback ratings. The methodology was grounded in the instrument development model, a variant of exploratory design with quantitative emphasis (qual ? QUAN). The specific methodology was modeled after validation of Porter et al.'s Val-Ed, a 360-degree instrument for school principals. In the qualitative phase, the instrument was developed and the researcher sought to understand the extent to which the assessment exhibited content validity, construct validity, and bias. The quantitative phase consisted of a pilot study to explore evidence for feasibility, reliability and internal validity of the CSIS-360. Feasibility measures revealed response rates of 89% for participants and 64% for nominated raters. Item completion rates were over 97% and standard errors of measurement were ± 0.25 rating points with 95% confidence. Reliability measures showed internal consistency reliability of 0.944 as measured by Cronbach's alpha coefficient. Validity measures showed moderate correlation between participant ratings and mean rater ratings and significant or highly significant correlations between all domain scale scores. Exploratory factor analysis revealed a six-factor solution accounting for 69.91% of the composite score variance. The pilot study was successful in developing and providing initial validation results for the CSIS-360 and demonstrated the instrument's potential for larger scale study. This study was a direct extension of previous research, aligned with research priorities in performance technology, and extended research in the area of 360-degree feedback by creating tools for feedback on the ISPI CSIS standards, validating a model, and expanding use of 360-degree assessments to informal leadership and influence roles of school improvement specialists. The results of this study help to bring human performance technology to the forefront of school improvement and provide a tool for reflection on improvement of school improvement competencies which could ultimately lead to improved school improvement outcomes. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]