<![CDATA[Critical thinking skills in Indonesia remain relatively low, as the country ranks 69th out of 80 countries. This affects students’ learning outcomes and analytical abilities in thinking. This study aims to determine the effectiveness of the Case Based Learning and Problem Based Learning models on critical thinking skills in drafting complaint letters. The research subjects were all 10th-grade students majoring in Office Management and Business Services at SMK Krian 2 Sidoarjo. The research design used was a Quasi-Experimental Nonequivalent Control Group Design. Data were collected using pre-tests, case studies, and post-tests. The data analysis technique used was descriptive analysis, encompassing data reduction, data presentation, and drawing conclusions, followed by a comparison test using the t-test. The results of the Paired Samples t-Test showed a Sig. (2-tailed) of 0.000 < 0.05, with a calculated t-value for the experimental class of -17.380 and for the control class of -25.782. The results of the Independent Samples t-Test showed a Sig. (2-tailed) value of 0.000 < 0.05, with the calculated t-value for the experimental class at -7.789 and for the control class at -7.818, indicating a significant difference. Furthermore, the N-Gain Score for the control class was 0.35 (moderate category), while the experimental class was 0.23 (low category). These results indicate that both the Case Based Learning and Problem Learning models both improved critical thinking skills in drafting complaint letters, as evidenced by a comparison of pre-test and post-test scores. However, in terms of effectiveness, Problem Based Learning was more effective than the Case Based Learning model. ABSTRAK Keterampilan berpikir kritis di negara Indonesia masih tergolong rendah karena berada di peringkat 69 dari 80 negara. Hal tersebut mempengaruhi pada hasil belajar dan kemampuan analitis siswa dalam berpikir. Penelitian ini bertujuan untuk mengetahui efektivitas model pembelajaran Case Based Learning dan Problem Based Learning terhadap keterampilan berpikir kritis dalam menyusun surat pengaduan. Subjek penelitian adalah seluruh siswa kelas X dengan Kompetensi Keahlian Manajemen Perkantoran dan Layanan Bisnis di SMK Krian 2 Sidoarjo. Jenis penelitian yang digunakan yakni ÂQuasi-Eksperimental desain Nonequivalent Control Group Design. Data dikumpulkan menggunakan soal pre-test, studi kasus, dan post-test. Teknik analisis data yang digunakan adalah analisis deskriptif mencakup reduksi data, penyajian data, penarikan kesimpulan dilanjutkan uji perbandingan menggunakan uji-t. Hasil uji Paired Samples t-Test menunjukkan nilai Sig. (2-tailed) sebesar 0.000 < 0.05 dengan hasil nilai t hitung kelas eksperimen sebesar -17.380 sedangkan kelas kontrol sebesar -25.782. Hasil uji Independent Samples t-Test menunjukkan hasil pada nilai Sig. (2-tailed) sebesar 0.000 < 0.05 dengan hasil nilai t hitung kelas eksperimen sebesar -7.789 dan kelas kontrol sebesar -7.818 menunjukkan terdapat perbedaan signifikan, selanjutnya hasil uji N-Gain Score kelas kontrol sebesar 0.35 dengan kategori sedang, sedangkan kelas eksperimen sebesar 0.23 dengan kategori rendah. Hasil tersebut menunjukkan bahwa model pembelajaran Case Based Learning dan Problem Based Learning keduanya mengalami peningkatan terhadap keterampilan berpikir kritis dalam menyusun surat pengaduan yang dibuktikan melalui uji perbandingan pada soal pre-test dan post-test. Namun pada aspek efektivitasnya, Problem Based Learning lebih efektif dibandingkan model pembelajaran Case Based Learning.]]>
