It has been eight years when the K to 12 Basic Education Curriculum was implemented in the country and Mother Tongue-Based – Multilingual Education (MTB-MLE henceforth) was inherent to its enactment. During this period, many issues have been raised concerning its overall impact specifically on the learning and acquisition of one of the most challenging content areas, the mathematical skills of each learner. This study explored the experiences of teachers on the development of numeracy skills of primary pupils using MTB-MLE. Teachers’ experiences on the development of numeracy skills among primary pupils through MTB-MLE were a smooth flow of instruction in Mathematics when MTB-MLE is used as an LOI, enhanced engagement to instruction showing confidence, interest and enjoyment on the lesson, enriched parent-teacher partnership in building numeracy among the learners, difficulties for some pupils to count in Bicol, and difficulties met in localizing, contextualizing and translating teaching materials for mathematics instruction. Strategies teachers use to develop numeracy skills of pupils using MTB-MLE along pedagogy were the use of locally-made materials or objects found in the community, exposing pupils to more drills and exercises, attendance to seminars is helpful, Differentiated Instruction (DI), using the manipulative, real and tangible object as instructional materials, translation, using collaborative approach teaching; along with learning engagement were play-based instruction, simple gifts as rewards and attractive and purposeful instructional materials through ICT; assessment of learning were differentiated assessment activities, and play-based assessment and observation. There were different learning activities implemented to develop numeracy particularly in Contextualization such as experiential learning; Translation such as English nursery rhymes in Bicol; Indigenization such as the use of local materials as instructional materials and Localization such as involving the community in the learning process. The gaps and issues encountered by teachers in developing literacy skills using MTB-MLE were the poor retention and low mastery of the four fundamental mathematical operations, complicating and varied learning competencies in the Curriculum Guide, and difficulties encountered by the pupils in mathematical problems.