In preparing the next generation of teachers, educator preparation programs (EPPs) are charged with the task of effectively merging theory and practice in the clinical setting. Partnered with a mentor teacher, the teacher candidate practices within an authentic, clinical setting. Guiding mentor teachers has been acknowledged as a necessary extension of EPPs, but little research exists on how to best provide access to training to all mentors. While online learning is a new delivery option in the field of clinical supervision, the use of an online training course provides mentor teachers with 24/7 access to an array of supports allowing for a better understanding of role and responsibilities. Dimensions of transformational leadership theory and constructivism provide a relevant framework to support the needs and outcomes of learning for mentor teachers. Through a qualitative, instrumental case study design, the study aimed to investigate the implementation of an online training course for mentor teachers and explore the impact of delivery on nine practicing mentors from the 2018–2019 academic year through the use of a questionnaire, a focus group, and semistructured interviews. Results indicated the responsibilities of a mentor teacher are vast and how mentor teachers acquire knowledge of role is diverse. With a consensus on the positive aspects of online learning, mentor teachers acknowledged how the use of the online platform aided in a better definition of role and responsibility and supported a validation of role importance in the collaborative guidance between mentor teachers and the EPP in the preparation of teacher candidates.