The article deals with the urgent issue of training high school students for external independent testing, the necessary condition for which is formation of their subject-matter competency, in particular, the mathematical one. The essence of competency-based approach, concepts “competence”, “competency” are revealed. The author singles out the effective forms, methods, technologies of organizing high school students’ educational activity in mathematics lessons aimed at quality preparation for external independent testing. Keywords: competency-based approach, competency, competence, subject-matter competency, external independent testing.