Purpose: This project aimed to develop, implement and evaluate a train-the-trainer initiative for community rehabilitation workers (CRWs) and rehabilitation specialists within a community rehabilitation program for children with delayed development in Tamil Nadu, India. Methods: Guided by the Knowledge to Action framework, non-governmental and academic partners collaboratively developed two 2-day workshops for (1) rehabilitation specialists and (2) CRWs. Outcomes were evaluated using mixed methods, with pre and 2.5-months post surveys (59 participants) and three focus groups (17 participants) involving trainers and trainees (including rehabilitation specialists and CRWs). Results: There were significant increases in the CRWs' self-perception of their capacity to assess comprehension, provide explanations, respond to questions, adjust teaching, motivate learners, communicate effectively, and provide feedback. Significant changes were noted for rehabilitation specialists in five of seven domains, and for rehabilitation specialist leads in six of seven domains. Participants appreciated the interactive training style, and the use of immersive methods such as role play, though noted challenges when instructions were unclear or when they felt that material was more theoretical. Conclusions: This collaboratively developed train-the-trainer project demonstrates the value of such an intervention, provides an example of how a tailored program can be developed, and suggests the importance of stakeholder-driven design processes.