Penelitian ini bertujuan mendeskripsikan keterlaksaan model pembelajaran, aktivitas peserta didik kelas XI, hasil keterampilan berpikir kritis, hasil belajar peserta didik, dan respon peserta didik terhadap model pembelajaran kooperatif tipe Group Investigation. Desain penelitian ini menggunakan one group pretest-posttest design. Instrumen penelitian terdiri dari lembar pengamatan keterlaksanaan model pembelajaran kooperatif tipe Group Investigation, lembar pengamatan aktivitas peserta didik, lembar pretest dan posttest peserta didik, lembar hasil belajardan lembar angket respon peserta didik. Hasil yang diperoleh antara lain (1) Keterlaksanaan sintaks model pembelajaran kooperatif tipe Group Investigationmemperoleh persentase nilai dengan kategori sangat baik dari fase 1 sampai penutup berturut-turut sebesar 91,67%; 91,67%; 92,71%; 91,67%; 89,59%; 95,83%; dan 90,27%. (2) Aktivitas peserta didik selama kegiatan pembelajaran kooperatif tipe Group Investigation pada materi asam basa dari pertemuan 1 sampai 3 berturut-turut sebesar 98,11%; 98,44%; dan 98,33%.(3)KBK peserta didik memperolehN-Gaindengan persentase pada keterampilan interpretasi kategori tinggi sebesar 93,33% dan 6,67% kategori sedang, inferensi kategori tinggi sebesar 86,67% dan 13,33% kategori sedang, dan analisis kategori tinggi sebesar 86,67% dan kategori sedang sebesar 13,33%.(4) Ketuntasan hasil belajar peserta didik kelas XI MI 3 memperoleh ketuntasan klasikan sebesar 90% peserta didik dalam kelas memperoleh nilai ≥75. (5)Respon peserta didik terhadap penerapan model pembelajaran kooperatif tipe Group Investigation pada materi asam untuk melatihkan keterampilan berpikir kritis mendapatkan hasil dengan kategori sangat baik sebesar 85,56%.

This study aims to describe the implementation of learning models, class XI students 'activities, the results of critical thinking skills, student learning outcomes, and students' responses to the Group Investigation cooperative learning model. This research design uses one group pretest-posttest design. The research instrument consisted of observations sheet on the implementation of the Group Investigation cooperative learning model, student activity observation sheets, student pretest and posttest sheets, student learning outcomes sheets and student questionnaire response sheets. The results obtained are (1) The syntax of the Group Investigation type of cooperative learning model obtains the percentage of scores in the excellent category from phase 1 to successive closing of 91.67%; 91.67%; 92.71%; 91.67%; 89.59%; 95.83%; and 90.27%. (2) Student activities during Group Investigation type cooperative learning activities on acid-base material from meetings 1 to 3 in a row amounted to 98.11%; 98.44%; and 98.33%. (3) KBK learners obtain N-Gain with a percentage in the interpretation skills of the high category of 93.33% and 6.67% of the medium category, inference of the high category of 86.67% and 13.33% of the medium category, and analysis of the high category amounted to 86.67% and the medium category was 13.33%. (4) Completeness of learning outcomes of students in class XI MI 3 obtained completeness by 90% of students in class receiving grades ≥75. (5) Learners' responses to the application of the Group Investigation type cooperative learning model on acid material to practice critical thinking skills get results with an excellent category of 85.56%.

Key Words:Cooperative Group Investigation type, Acid Base, CBC.