This study investigates the effectiveness of the Mother Tongue- Based Multilingual Education (MTB-MLE) Certificate Program to the academic achievement of pupils utilizing their first language in learning. Teacher-scholars’ performance was measured in terms of teaching-learning and teaching facilitation. Moreover, pupils’ satisfaction levels were determined based on the comparison of teachers’ performance as scholars, trained and non-trained. The findings of this study revealed that teacher-scholars who enrolled in the certificate program showed positive and direct effect to pupils’ academic achievement. An increase of pupils’ achievement and satisfaction level towards learning using MTB-MLE as a medium of instruction was grounded on the intensity of teachers’ training about the implementation of MTB-MLE in each grade level. Furthermore, scrutinizing the differences of both teachers’ performances and pupils’ performances in Grades 1 to 3 werehelpful in determining more provisions to make the K to 12 implementation more effective and more understandable to individuals within the cycle of learning.