ABSTRACT There is a national shortage of young people entering and remaining in STEM majors and careers. In addition, there are certain subgroups of youth particularly underrepresented in STEM including girls, youth with a disability, youth living in a low-income family, youth who are or will be first-generation college students, and youth from an ethnic or racial minority group. One promising strategy to excite, recruit, and retain youth in STEM is to offer them the opportunity to participate in a STEM mentoring program. Pre-match mentor training has been shown to support the development of close and longer-lasting mentoring relationships; however, no mentor training specific to issues relevant to STEM mentoring of youth exist. The main purpose of this project is to develop new mentor training lessons based on research associated with STEM recruitment that build upon previous successes in providing core, pre-match, web-based mentor training. In addition to tailoring mentor training to the needs of training mentors in skills related to STEM success, training directors of mentoring programs, more generally, have requested the ability to customize online training to meet the unique needs of their program, sometimes adding lessons and sometimes deleting those that may not be relevant to their program model or requirements. A second goal of this project is to enhance the flexibility of iRT’s eTrove, a learning (LMS) and project management software platform, to allow diverse STEM mentoring programs to create custom training for their volunteer mentors. In Phase 1, two pre-match mentor training lessons will be created based upon the practice experience of the PI’s, key informant interviews with STEM mentoring professionals, and a comprehensive literature review conducted by two of the investigators. In addition, custom course creation functionality will be programmed into the eTrove LMS and alpha tested. Once the lessons and LMS enhancements have been programmed and alpha tested, STEM mentoring program staff members (N = 5) will individually test the usability of the software in a One-to-One Evaluation Study. After any software errors or usability problems are addressed, a Feasibility Study testing both the training and the new software functionality will be conducted with staff from eight STEM mentoring programs and three mentors from each program. Pending reaching benchmark outcomes in Phase 1, Phase 2 will have the goal of creating six additional lessons related to successful STEM mentoring, increasing the flexibility in the LMS course customization functionality adding administrative features to the dashboard; enhancing individual and cross- mentor reporting features for match support staff members and evaluators.