Training and consultation are core implementation strategies used to support the adoption and delivery of evidence-based prevention programs (EBPP), but are often insufficient alone to effect teacher behavior change. Group-based motivational interviewing (MI) and related behavior change techniques (BCTS; e.g., strategic education, social influence, implementation planning) offer promising adjuncts to training and consultation to improve EBPP implementation. Beliefs and Attitudes for Successful Implementation in Schools for Teachers (BASIS-T) is a theoretically-informed, group-based, motivational implementation strategy delivered prior to and immediately after EBPP training. The purpose of this study was to examine the proximal effects of BASIS-T on hypothesized mechanisms of behavior change (e.g., attitudes, subjective norms, intentions to implement) in the context of teachers receiving training and consultation for the Good Behavior Game. As part of a pilot trial, 83 elementary school teachers from 9 public elementary schools were randomly assigned to a BASIS-T (n = 44) or active comparison control (n = 39) condition, with both conditions receiving GBG training and consultation. Theorized mechanisms of behavior change were assessed at baseline and immediately post-training to examine the proximal effects of BASIS-T. A series of mixed effects models revealed meaningful effects favoring BASIS-T on a number of hypothesized mechanisms of behavior change leading to increased motivation to implement GBG. The implications, limitations, and directions for future research on the use of group-based MI and other BCTs to increase the yield of training and consultation are discussed. [This paper was published in "Prevention Science" v22 p722-736 2021.]