This qualitative research brought to light the mathematics skills manifested by the high school students in one public secondary school in the Fifth District of the Province of Iloilo. Five participants were purposively selected with the use of the checklist of non school activities. Case study of multiple cases was used to determine the non-school activities of the high school students, the mathematics skills that they manifested in their non-school activities, and the ways of learning those mathematics skills. The principles of subjectivism and interpretivism backed up the thematic and cross-case analyses of data. Interview, observation, and journal were used to triangulate the results. Though the participants were exposed to varied experiences in life , the findings revealed that they also had common livelihood activities which were taking care of animals, taking care of mini store, gardening and planting trees. It was also found out that they were involved in household chores, like cooking rice and viand, washing clothes and dishes, cleaning the house, fetching water, and taking care of younger brother, sister, cousin, or niece. They were also attracted by ball games, card games, board games, computer games, racket game , and Laro ng Lahi. It was further revealed that the mathematics skills manifested by the participants as they engaged in their non-school activities were: selecting tools and computational strategies, reasoning, problem solving, representing ideas, and communicating ideas. Computational strategies dominantly used were: counting, calculating, estimating, and measuring. There were differences in the participants' ways of learning mathematics skills. They learned through the practices of the family, through the influence of the school, and through social interaction in the community. Consequently, however, those ways could be grouped into one theme: "Learning through Example and Hands-on Experience". Embedded in the discussion of the results and recommendations are the potentials of non-school activities in teaching mathematics skills.