This study aims to: (1) improve learning activities by means the implementation of the two stay-two stray instructional model, and (2) improve the learning achievement Social Studies of class IX-A, SMP Negeri 1 Sidamanik Sumatera Utara. This study is classroom action research (CAR) consisting of two cycles, using Kemmis & Taggart design. The data collection techniques used were observation, achievement test, and documentation. The data analysis used the quantitative descriptive. The results are as follows. (1) The implementation of media-aided two stay two stray instructional model in social studies teaching can enchance learning activities and learning achievement. There is an increase in students' learning activities: in the precycle, only 55.56%, in cycle I, the average score of students' activities was 59.10 % and it became 85.50% in cycle II. (2) There is an increase in students' the average of learning achievement: in the precycle, only 68.61, in cycle I, the average score of of learning achievement was 71.94 and it became 82.10 in cycle II. There is an increasing mastery of classical learning. In the precycle, only 58.33% of students achieved learning mastery, in cycle I, it became 77.78%, and in cycle II, it became 100%.