It is important for all professionals who work with individuals who have ASD to have sufficient knowledge of the disorder. The development of ASD knowledge may occur during preservice training and/or through professional development. Currently, there is no "gold standard" measure of ASD knowledge. A study focusing on the development of a reliable and valid measure of ASD knowledge for practitioners and preservice professionals is warranted. To address this need, the current study provides preliminary information on the development and preliminary validation of the Autism Spectrum Knowledge Scale Professional Version-Revised (ASKSP-R) with a sample of school-based professionals (N = 427). Results suggest the ASKSP-R is a univariate measure with good reliability. Implications and suggestions for future research are discussed.