As the transition period from primary to secondary education is difficult for many students, our strive is to study the psychological features, which may scaffold student’s promotion and provide for future successful learning. We consider the educational media to be a complex system of psychological features, which depend on the content of education and the way, in which the educational process is organized. The “activity-and-content oriented” educational media devised after theoretical principles of the Developmental Instruction (Davydov), according to our hypothesis, provides sound bases for primary competencies formation, which are vital for secondary education. To test this assumption, we have diagnosed the quality of reflection, analysis, planning, model-acquisition and model-application, achieved by 204 students from two different educational media (“activity-and-content oriented” and “knowledge oriented”). For assessment purposes two diagnostic tools were used: “Transpositions” and “Moon” test. Both tests exploited contexts, which were unfamiliar to both groups of students. The results show, that students from the “activity-and-content” oriented educational media performed significantly better in most cognitive primary concepts. We consider these findings to support our major hypothesis, that educational media is a powerful source to scaffold students’ primary competencies’ formation, which in its turn provides for successful learning in secondary school.