This study examined factors affecting the implementation of Mother Tongue-Based Multilingual Education (MTB-MLE) as perceived by teachers in Baguio and Benguet, Philippines. The implementation of using local mother tongues as the medium of instruction for kindergarten through 3rd grade is a new policy in the country starting in 2011. The researchers conducted a study to understand implementation challenges from the teacher perspective. Overall, teachers had positive views of using mother tongues in the classroom and felt students' language acquisition and cognitive development improved. However, teachers also struggled with lack of training and limited teaching resources to support using the new mediums of instruction.