This study focused on developing a valid and reliable instrument that can not only identify successful co-teaching, but also the professional development needs of co-teachers and their administrators in public schools. Two general questions about the quality of co-teaching were addressed in this study: (a) How well did descriptors within each of four hypothesized survey constructs interrelate and represent specific intended constructs? and (b) did differences in perception of co-teaching quality exist among various subgroups of teachers and administrators based on their roles and experiences regarding co-teaching? Factors that emerged from an exploratory factor analysis of a pilot study served as the main conceptual framework of this research. Based on review of the pattern of factor loadings and other technical analysis, the present survey was finalized. Revised items were then tested with 234 public school teachers. Findings revealed evidence supporting both reliability and validity of the survey instrument which was interpreted to support its use to inform future research on co-teaching. Reliability measures indicated an overall alpha of 0.95 for all 42 items; with alpha's ranging from 0.76 to 0.91 for the four factors. Validity measures were 0.84 for the Standardized Root Mean Residual and 0.95 for the Comparative Fit Index. In addition, insights gained through the analysis of differences among respondent subgroups were interpreted to suggest possible applications to inform professional development in co-teaching. In general differences across the groups suggest that the groups do not consistently agree upon what constitutes successful co-teaching. [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.]