The main purpose of this study was to explore the factors of Mathematics achievement of the students from their own perspectives. Mixed-methods approach was used in the study. The quantitative part was employed to define the level of Mathematics achievement of the students. On the other hand, the qualitative part of the study explored the student-related and teacher-related factors of the students’ mathematics achievement. The participants of the study were the 247 and 10 of these Grade 7 students of Moonwalk National High School who are officially enrolled for the School Year 2019-2020. Qualitative data were gathered through a 6-item open-ended questionnaire developed by the researcher and through a Focus Group Discussion attended by ten selected students. Whereas, quantitative data were the first quarter GPA of the participants in their Mathematics class. Data analysis involved mean, standard deviation, frequency and percentage for quantitative data while thematic analysis and a simple document analysis were employed for qualitative data. Results show that most of the Grade 7 students have fairly satisfactory achievement in Mathematics. Analysis of the qualitative data shows that student-related factor of Mathematics achievement include interest, self-confidence, attitude towards Math, motivation, perseverance and commitment, compliance, attendance, class participation, study habits, peer support, family support, technology aided learning, asking questions, math self-concept, math anxiety, talkativeness, English language comprehension, concentration/focus, health condition and nutrition, and computer gaming. Moreover, students reported that teacher-related factors of their mathematics achievement include traits such as being kind, energetic, strict, cheerful, positive, hardworking, patient, confident and responsible. Results further reveal that teacher’s humor, motivation towards students, competence, mastery of content and teaching methods and strategies such as the use of varied learning activities (e.g. songs, manipulatives, games, etc.), code-switching, good explaining strategy, and collaborative learning positively contribute to their Mathematics achievement. However, teacher’s anger, yelling at students, teaching too fast, teaching more than one lessons a day, teaching different lessons everyday and workload were reported by the students as factors that negatively influenced their Mathematics achievement. In addition, curriculum and noisy learning environment were other factors found to negatively impact mathematics achievement. As a result, teachers are encouraged to have awareness and to take into consideration these various factors that help and hinder their students’ achievement in Mathematics.