To help teachers develop a repertoire of instructional strategies that will effect positive changes on students' learning outcomes is essential for both general education and the field of gifted education. This article introduces readers to a classroom observation tool that is designed to help assess professional development needs of teachers of gifted learners in practicing differentiation best practices. The authors give an extensive review of the literature, discuss the blueprint for constructing the scale, and provide a detailed description of the scale development process, the technical adequacy data of the instrument, as well as how the instrument can be used in multiple settings. The authors also draw implications for using this tool to connect the instructional efficacy of teachers to student learning outcomes. (Contains 5 tables.)