Highly prevalent mental health needs among youth necessitate the use of evidence-based practices (EBPs). However, EBPs are inconsistently implemented in their primary service delivery setting, schools. Educators' and School-based clinicians' motivation and beliefs often hinder their EBP adoption. Beliefs and Attitudes for Successful Intervention in Schools (BASIS) is a theory-informed, group-based, pre-implementation strategy that blends Motivational Interviewing (MI), Strategic Education, and Social Influence techniques shown to improve individual behavior change mechanisms and evidence-based practice (EBP) adoption. MI techniques (e.g. elicit change talk, build an action plan) are integrated throughout BASIS sessions (n= 2; group 3-10), including facilitator-mediated technical aspects (e.g. elicit change talk with open-ended questions, reflect on participant experiences); and individually oriented and small group workbook activities (e.g. setting an intention, problem-solving, planning). As part of a large-scale cluster-randomized control trial simultaneously examining the effectiveness of BASIS and Trauma-Focused Cognitive Behavioral Therapy (TF-CBT), BASIS was delivered via the web by a community-based facilitator to 47 school-based mental healthcare (SBMH) practitioners serving 47 schools in six states. In this paper, we describe the BASIS fidelity elements of content adherence (Aim 1); comprehensiveness, facilitation supports, facilitator competence, and participant responsiveness (Aim 2); and explore the variability and associations between fidelity elements (Aim 3). Overall fidelity elements were high, and closer analysis revealed that adherence and responsiveness were associated. These exploratory findings point to a need for future research to describe and analyze fidelity elements of BASIS other group-based MI-embedded supports, particularly for complex or comprehensive web-based MI-delivery.