Permasalahan yang ada pada peserta didik kelas IX-B SMP XYZ Sentani, Papua adalah rendahnya pencapaian hasil belajar kognitif. Faktor-faktor yang mempengaruhi peserta didik kesulitan mencapai hasil belajar kognitif berasal dari dalam dan luar diri peserta didik. Melihat masalah yang ada, peneliti memberikan solusi dengan menerapkan penggunaan lembar kerja siswa (LKS) sebagai media pembelajaran dalam meningkatkan pencapaian hasil belajar kognitif. Tujuan penelitian ini untuk mengetahui pencapaian hasil belajar kognitif peserta didik melalui penggunaan media lembar kerja siswa (LKS) dan untuk mengetahui cara penggunaan media lembar kerja siswa (LKS) dalam membantu peserta didik mencapai hasil belajar kognitif. Metode penelitian yang digunakan adalah metode penelitian tindakan kelas (PTK) yang berlangsung selama dua siklus. Penelitian dilaksanakan di SMP XYZ Sentani, Papua kelas IX-B tanggal 26 Agustus 2015 hingga 13 November 2015. Instrumen penelitian yang digunakan berupa lembar penilaian LKS, lembar tes tertulis, lembar observasi, lembar angket, dan lembar wawancara. Berdasarkan hasil penelitian, penggunaan media lembar kerja siswa belum dapat meningkatkan pencapaian hasil belajar kognitif peserta didik dari siklus 1 ke siklus 2. Terjadi penurunan presentase pencapaian hasil belajar peserta didik pada dimensi proses kognitif kedua (memahami). Akan tetapi, penggunaan LKS dapat meningkatkan proses belajar kognitif peserta didik./ The problem faced by the students in grade IX-B SMP XYZ Sentani Papua is the lack of acheivment in cognitive learning outcomes. The factors that affected the students in having a difficulty reaching the cognitive study results were internal and external. Seeing the problem at hand, the researcher tried to provide a solution by applying the use of student worksheets as a medium in achieving the cognitive learning outcomes. The purpose of the research is to know the acheivments in cognitive learning outcomes in the students using student worksheet as a media and know the way to use student worksheet as a media to aid students in achieving the cognitive learning outcomes. The research methodology used is Class Action Research (CAR) that lasted for two cycles. The research was carried out in XYZ Junior High School Sentani, Papua grade IX-B from August 26, 2015 until 13 November, 2015. The research instruments used are student assesment worksheet, written test sheet, observation sheet, questionnaire sheet, and interview sheet. Based on the results of the research, using student worksheets media has not been able to improve the cognitive learning outcomes of the students from cycle 1 to cycle 2. There was a decline in the percentage of the cognitive learning outcomes of the students on the dimension of the second cognitive process (understanding). However, the use of student worksheets can improve the cognitive learning process of the students.