Training prior to implementing evidence-based interventions (EBIs) is essential to reach high levels of fidelity. However, the time and cost of in-person training are often barriers to implementation. Online learning offers a potential solution, though few studies examine the relationship between online training and fidelity of implementation. This study explored whether teachers trained online have similar levels of adherence, dosage, quality of delivery, and student responsiveness compared to teachers trained in-person on the Botvin LifeSkills Training (LST) middle school program, a universal prevention intervention proven to reduce substance use and violence, as part of a national dissemination project. This study involved a sample of 989 LST teachers across 114 school districts, representing 296 schools in 14 states. All teachers were first trained in LST implementation between 2016 and 2019. Hierarchical linear models were used to assess relationships between training modality and the four fidelity outcomes. Online training was associated with lower ratings of quality of delivery compared to in-person training, but no significant associations existed between online training and adherence to the curriculum, dosage, or student responsiveness. Findings from this study generally indicate that online training builds competencies important for school-based EBI implementation, while also highlighting potential shortcomings related to quality of delivery. Ensuring the inclusion of experiential learning activities (e.g., practice delivering content, receiving feedback on delivery) may be key to quality of delivery as online trainings for facilitators of school-based EBIs evolve.