This study aimed to determine the relationship between the teachers’ competence and students’ academic achievement in science, as well as investigating the effect of teachers’ demographic profile in both dependent variables. The respondents were the total population of science teachers in Davao City National High School with teaching positions I-III. A descriptive-comparative and correlation survey method was utilized. Independent samples t-test, Analysis of Variance (ANOVA), and Pearson-r Correlation were the statistical treatments used in the study. The teacher-respondents answered a combined adopted and teacher-made survey questionnaire in gathering the data. Findings of the study showed that most of the science teachers are female having teaching positions I, where teaching experience were mostly less than ten years and majority have more than one ancillary function. Additionally, it revealed that science teachers teaching competence was at integrating level whereas students’ academic achievement was very satisfactory. Moreover, result showed that there was no significant difference among teaching competence in terms of their sex, teaching position, and teaching experience excluding the number of their ancillary function that is significantly different. Students’ academic achievement was significantly different in terms of teachers’ teaching position, teaching experience, and ancillary function excluding sex. Thereby, teaching competence was highly and positively associated with students’ academic achievement in science. Findings of the study recommended to establish reasonable guidelines in the distribution of ancillary functions and make best use of school existing programs like School Learning Action Cell (SLAC) to ameliorate teaching competence and students’ academic achievement.