Purpose <p>The current study aims to expand on existing psychometric information related to the Autism Spectrum Knowledge Scale Professional Version-Revised (ASKSP-R; McClain et al., 2019). Specifically, the study addresses two research questions: (1) Which items on the ASKSP-R show evidence of differential item functioning (DIF) between school psychologists (SPs) and speech-language pathologists (SLPs)? and (2) To what extent do ASKSP-R score distributions differ between SPs and SLPs?</p> Method <p>Differential item functioning analysis was used to assess whether items in the measure function similarly across two groups with comparable levels of autism knowledge. Data were collected as part of a larger project examining the current state of autism knowledge among school-based professionals that frequently work with autistic children. The sample included in the study consisted of School Psychologists (<i>n</i> = 210) and Speech-Language Pathologists (<i>n</i> = 202) who completed a demographic questionnaire and the ASKSP-R measure.</p> Results <p>Results indicated that two items (14 &amp; 15) functioned differently across the two professional groups.</p> Conclusion <p>Potential explanations for item bias are discussed pertaining to training differences and focus of knowledge areas, along with suggestions for revising the measure.</p>