The related constructs of opportunity to learn (OTL) and achievement growth are fundamental aspects of the current large-scale assessment and accountability system in operation in the United States. For purposes of this article, OTL is defined as the degree to which a teacher dedicates instructional time and content coverage to the intended curriculum objectives emphasizing high-order cognitive processes, evidence-based instructional practices, and alternative grouping formats. Both OTL and achievement growth, although frequently talked about by education policy makers and teachers, are actually difficult to measure. Much of my research, in collaboration with other colleagues, over the past decade has concerned the measurement of these constructs in ways that facilitate teachers' understanding of them and to advance sound policies regarding the instruction and assessment of students with disabilities (SWDs). In this article, I examine both the measurement of OTL and achievement growth, share recent research on them, and outline an agenda for future research on these two important aspects of standards-based accountability systems for all students.