Abstract. Curriculum is the best instrument in the school to attain the learning goals in the nation. One of the most important facets in the K to 12 Curriculum is crafting the curriculum applicable to the learners. Hence, the teachers are fully aware on these standards and principles; but few are implementing it. Many claimed that they are implementing it, but some of them have the difficulty in implementing it effectively. To implement these principles of the lessons effectively, this research was to investigate the experiences of Mathematics teachers on Contextualization and Localization of lessons in Mathematics in the Division of City of Bogo, Cebu Province towards developing a substantive theory.
The researcher utilized a constructivist approach by Charmaz in grounded theory. An example of sixteen participants was selected allowing the development of a substantive theory. This substantive theory impacts with the students, teachers, school heads, and DepEd teaching personnel. This is realized through exploring and analyzing which the teachers experience contextualization and localization of lessons in Mathematics through the perceptions of the teacher’s instructional competence, the community adaptation and the student’s engagement.
With these perceptions, teachers can present the lesson in a more meaningful learning experiences and relevant context based on the learner’s previous experiences and real-life situations. Both of which adhere in making the class adaptable, suitable, original, pertinent, important, and adoptive to students’ level of awareness and educational needs.

Keywords: curriculum, contextualization, localization, grounded theory,
Constructivist approach, experiences, Mathematics