The study investigated the impact of different factors on teaching competencies in secondary education. The study was conducted with a survey of 1,256 junior and senior high schoolteachers in the Northwest mountains of Vietnam. The data obtained was tabulated, analyzed and interpreted by using the statistical techniques of mean, standard deviation average rating, T-test and Analysis of Variance (ANOVA), to reveal the variables that most affect teacher competence in the Northwest mountains, and to identify seven factors that most affect the competence of teachers. These identified factors are internal factors (gender, age, major, experience, and race), and external factors, namely the distances to school, school facilities, and culture.