Penelitian ini didasarkan atas hasil observasi yang menemukan bahwa sebagian besar siswa memiliki pemahaman konsep yang rendah.Pembelajaran kooperatif tipe STAD (Student Team Achievement Division) dicoba untuk diterapkan. Penerapan STAD diharapkan dapat mencapai tujuan penelitian yaitu meningkatkan pemahaman konsep melalui penerapan STAD dan mengetahui langkah-langkah pembelajaran kooperatif tipe STAD dalam meningkatkan pemahaman konsep. Penelitian ini adalah penelitian tindakan kelas (PTK) dengan model Kemmis dan Taggart yang berlangsung selama 03 Agustus 2015 - 21 September 2015 di kelas VIII di sekolah ABC. Penelitian dilakukan dengan tiga siklus dengan melibatkan 32 siswa. Adapun instrumen yang digunakan dalam pengumpulan data yaitu lembar tes, lembar LKK kelompok, lembar observasi terbuka, lembar angket, lembar umpan balik mentor, lembar wawancara siswa dan mentor, dan jurnal refleksi. Berdasarkan analisis data, diperoleh bahwa penerapan tahapan pembelajaran kooperatif tipe STAD (Student Team Achievement Division) mampu meningkatkan pemahaman konsep siswa kelas VIII pada topik relasi dan fungsi./ Based on observation researcher that found out that most of students have a low level of conceptual understanding. In order to solve this problem, the researcher applied cooperative learning method, called STAD (Student Team Achievement Division). The researcher expected the implementation of STAD will be able to achieve the research’s purpose to increase the conceptual understanding and know the steps of the cooperative learning method type STAD in order to increase the conceptual understanding. This research is Classroom Action Research (CAR) model Kemmis & Taggart, which took place on August 3, 2015 – September 21, 2015 of the 8th grade students at ABC school. This research was done in three cycles that involved 32 students. The instruments used to collect the data were test sheets, group worksheets, observation sheets, interview sheets, mentor’s umpan balik sheets, interview sheets from students and mentor, and reflection journals. Based on the data analysis, the researcher found out that the implementation of cooperative learning method type STAD (Student Team Achievement Division) is able to increase concept understanding of 8th grade students in relation and function topic.