This study aims to develop and review the effectiveness of learning student worksheet based on the AL-MASTER model to improve students' critical thinking skills. The research was conducted at SMP Negeri 1 Purbolinggo. This type of research is research and development or Research and Development (R&D). The research and development process includes four stages: defining, planning, developing, and disseminating. The analysis included (1) data analysis of questionnaire validation of teaching materials and respondents and (2) analysis of critical thinking ability test data. The results of the analysis show that after using the AL-MASTER Model-based LKPD, it can be concluded that (1) The average results of expert assessment of the feasibility level of product development are in the feasible category, (2) The results of product trials and reviewing students' critical thinking skills show an increase in the Pre-Test average and the Post-Test average in class VIII.1 and the results of the N-gain percentage for that class were 68.74% with quite effective criteria, (3) Learning showed that time efficiency in class VIII.1 was quite efficient and the percentage of completeness in the experimental class was 74.17% or 26 students complete while the percentage of completeness, and (4) the response of teachers and students in the category was exciting.Penelitian ini bertujuan untuk mengembangkan dan meninjau efektifitas pembelajaran lembar kerja peserta didik (LKPD) berbasis model AL-MASTER untuk meningkatkan kemampuan berpikir kritis peserta didik. Penelitian dilaksanakan di SMP Negeri 1 Purbolinggo. Jenis penelitian ini merupakan penelitian dan pengembangan atau Research and Development (R&D). Proses penelitian dan pengembangan meliputi empat tahapan yaitu: pendefinisian, perencanaan, pengembangan, penyebaran. Analisis yang dilakukan mmeliputi (1) analisis data lembar angket validasi bahan ajar dan responden, dan (2) analisis data tes kemampuan berpikir kritis. Hasil analisis menunjukkan bahwa setelah penggunaan lembar kerja peserta didik berbasis Model AL-MASTER diperoleh simpulan bahwa (1) Hasil rerata penilaian ahli terhadap produk pengembangan tingkat kelayakan dalam kategori layak, (2) Hasil ujicoba produk dan meninjau kemampuan berpikir krtisi peserta didik terdapat peningkatan rerata Pre-Test dan rerata postest pada kelas VIII.1 dan hasil persentase N-gain untuk kelas tersebut sebesar 68,74% dengan kriteria cukup efektif, (3) Pembelajaran menunjukan bahwa efisiensi waktu pada kelas VIII.1 cukup efisien dan persentase ketuntasan kelas eksperimen sebesar 74,17% atau 26 peserta didik tuntas sedangkan persentase ketuntasan, dan (4) Respon guru dan peserta didik daam kategori sangat menarik.