Producing local materials is a challenge to mother tongue education programs especially in linguistically diverse contexts. To address this, a five-day teacher training program on materials localization for K-3 teachers in a linguistically diverse area in the Philippines was designed and implemented. The program was based on frameworks about materials localization and development, needs analysis data, and curricular and materials guidelines from the Ministry of Education. The program, implemented through the collaboration of stakeholders, capacitated teachers in localizing the language and culture in a set of lessons from Ministry-produced textbooks. These were evaluated and shown to have met standards of high-quality, localized materials. Results suggest that the designed program is a feasible grass-roots platform for localizing materials. The presented program design and activities, as well as the good practices and lessons learned from the implementation, are instructive to program implementers in linguistically diverse contexts.