As specialized instructional support personnel begin learning and using motivational interviewing (MI) techniques in school-based settings, there is growing need for context-specific measures to assess initial MI skill development. In this article, we describe the iterative development and preliminary evaluation of two measures of MI skill adapted from the substance abuse field for use in school-based settings. We developed the Video Assessment of Simulated Encounters for School-Based Applications and the Written Assessment of Simulated Encounters for School-Based Applications to evaluate the initial MI skill development of school-based personnel participating in a multi-component, MI training program. Preliminary psychometric evidence supports continued development and refinement of the measures.