Kindergarten through 12th-grade classrooms is almost exclusively inclusive instructional settings. Supports for the regular education teachers vary as time and budgets permit, placing increased responsibility for providing instruction to children with disabilities on these teachers. Professional development targeted at teachers' self-efficacy with respect to inclusion best practices should be provided, with such efforts informed by the specific needs of the participants. This paper presents an investigation of the implementation of a measuring instrument for that purpose with findings and implications for guiding professional development.