The study determined the level of grammatical competence of 177 Junior High School students and on the design and development of a supplementary learning material to enhance the grammatical competence of the students along subject-verb agreement. The study revealed that students favored textbooks as their preferred reading material at home. They are also exposed to various media types, with denser exposure to books and television. The students' parents are generally at par in their highest educational attainment, which vary across cases of being either graduate or undergraduate in College, High School and Elementary School levels. Majority of the students' fathers are High School graduate, parallel to the educational attainment of their mothers. The study concludes that the Junior High School students need to further enhance their level of grammatical competence in subject-verb agreement. The merits and essentials of the findings were drawn and treated as inputs in the development of a supplemental learning material in subject-verb agreement. The study offers a set of recommendations to improve strategies and techniques in instruction and in the development of instructional materials that will complement the goal to develop the relevant competencies of students in the field of English language learning.