The Council for the Accreditation of Educator Preparation (CAEP) requires faculty from educator preparation programs to provide evidence of credential candidates' impact on K-12 student learning. However, there is a paucity of information on preparation programs' use of direct assessments of student learning to gauge credential candidate effectiveness and engage in a continuous cycle of program improvement. Rather, measures of impact consist primarily of indirect estimates, such as results from licensure exams, supervisor evaluations, and classroom observations. This article describes the use of single-subject research design as a method of assessing the impact of credential candidates on K-12 student learning, especially as it relates to meeting the instructional and behavioral needs of diverse students. Implications for how this evaluation approach may be applied to a wide array of commonly targeted K-12 student skills, and employed within a broader program evaluation system are discussed.