Proses pembelajaran harus menggunakan pendekatan saintifik, dalam pendekatan saintifik siswa diharapkan memiliki berbagai keterampilan salah satunya keterampilan berpikir kritis. Keterampilan berpikir kritis sangat penting untuk dilatih selama pembelajaran dikelas, karena siswa dengan kemampuan berpikir yang baik mampu memberi dampak dalam penyelesaian masalah dengan strategi yang tepat. Oleh karena itu, siswa membutuhkan model pembelajaran yang tepat pada proses peningkatan keterampilan berpikir kritis siswa. Penggunaan model pembelajaran Open-Ended dapat menjadi inovasi bagi guru dan siswa. Adapun tujuan dari penelitian ini adalah untuk mengetahui bagaimana aktivitas guru, aktivitas siswa dan keterampilan berpikir kritis siswa melalui model pembelajaran Open-Ended di kelas IV SDN Utama 1 Tarakan. Jenis penelitian yang digunakan yaitu Penelitian Tindakan Kelas (PTK) yang meliputi empat tahapan yaitu: perencanaan, pelaksanaan, pengamatan, dan refleksi yang dilakukan dalam dua siklus dengan subjek penelitian berjumlah 28 siswa. Teknik pengumpulan data mengenai keterampilan berpikir kritis dengan menggunakan instrument tes, lembar observasi dan lembar wawancara. Hasil tes keterampilan berpikir kritis siswa dalam aspek kognitif pada siklus I yang diperoleh sebesar 53,57%, hasil pengamatan aktivitas siswa dalam aspek afektif dan psikomotorik siklus I dengan jumlah presentase keseluruhan adalah 81,47%, hasil pengamatan aktivitas guru siklus I dengan presentase 81,25%. Masuk pada siklus II hasil tes keterampilan berpikir kritis siswa dalam aspek kognitif sebesar 98,85%, hasil pengamatan aktivitas siswa dalam aspek afektif dan psikomotorik siklus II dengan presentase 89,81%, hasil pengamatan aktivitas guru siklus II dengan presentase 91,07% terdapat peningkatan keterampilan berpikir kritis siswa dari siklus I ke siklus II. Peningkatan nilai hasil tes keterampilan berpikir kritis siswa dihitung secara klasikal sebesar 45,27%. Jadi dapat disimpulkan penerapan model pembelajaran Open-Ended dinyatakan layak dan dapat meningkatkan keterampilan berpikir kritis siswa dalam proses pembelajaran. Kata Kunci : Keterampilan Berpikir Kritis, Model Pembelajaran Open-Ended

The Learning process must use a scientific approach, in the scientific approach students are expected to have various skills, one of which is critical thinking skills. Critical thinking skills are very important to be trained during class learning, because students with good thinking skills are able to have an impact on problem solving with the right strategy. Therefore, students need the right learning model in the process of improving students' critical thinking skills. The use of an Open-ended learning model can be an innovation for teachers and students, The purpose of the research was to determine the teachers activity, the students activity and students' critical thinking skills through the Open-Ended learning model at class IV SDN Utama 1 Tarakan. the type of research was Classroom Action Research (CAR) which comprises four stages, namely: planning, implementation, observation, and reflection. These stages are executed in two cycles, encompassing a total of 28 research subject. The techniques of data collection regarding critical thinking skills used tests, observation sheets and interview sheets. The results of the students critical thinking skill test in the cognitive aspect in cycle I obtained were 53.57%, the results of observations of students activity in the affective and psychomotor aspects of cycle I with the total percentage was 81,47%, the results of observations of teachers activity cycle I with a percentage of 81,255. entering in cycle II the results of the students critical thinking skills test in the cognitive aspect amounted to 98,85%, the results of observations of student activity in the affective and psychomotor aspects of cycle II with a percentage of 89,81%, the results of observations pf teachers activity in cycle II with a percentage of 91,07% there was an increase in students' critical thinking skills from cycle I to cycle II. The increase in the value of students' critical thinking skills test results was calculated classically by 45,27%. It can be concluded that the application of the Open-ended learning model is declared feasible and can improve students' critical thinking skills in the learning process. Keywords: Critical Thinking Skills, Open-Ended Learning Model