Penelitian bertujuan untuk mengetahui efektivitas model pembelajaran problem based learning dengan asesmen portofolio pada materi sistem imun ditinjau dari hasil belajar siswa di SMA N 3 Demak. Penelitian quasi eksperimen dengan rancangan penelitian pre-test post-tes control group design. Populasi penelitian seluruh siswa kelas XI MIA SMA N 3 Demak, pengambilan sampel dengan purposive sampling. Sampel penelitian siswa kelas XI MIA 3 sebagai kontrol dan siswa kelas MIA 4 sebagai eksperimen. Variabel bebas berupa model pembelajaran dan variabel terikat berupa hasil belajar, kelas eksperimen menggunakan model problem based learning sedangkan kelas kontrol menggunakan model ceramah-diskusi. Efektivitas penggunaan problem based learning dipadukan asesmen portofolio terhadap hasil belajar siswa dianalisis dengan N-Gain, independent sample t test dan ketuntasan klasikal. Hasil penelitian menunjukan peningkatan aspek kognitif kelas eksperimen lebih tinggi dibandingkan dengan kontrol, hasil belajar kelas eksperimen dan kontrol berbeda signifikan, dan ketuntasan klasikal eksperimen lebih dari 80 %. Simpulan penelitian model problem based learning dengan asesmen portofolio efektif diterapakan pada materi sistem imun.
The research aims to determine the effectiveness of problem based learning models with portfolio assessment on the immune system subject in terms of student learning outcomes in SMA N 3 Demak. A quasi-experimental research with a post-test control group design pre-test design. The population is all students of class XI MIA SMA N 3 Demak, taking samples with purposive sampling. The research samples are students of class XI MIA 3 as controls and students of MIA 4 class as experiments. The independent variable is a learning model and the dependent variable is learning outcomes, the experimental class uses a lecture-discussion model while the control class uses a problem based learning model. The effectiveness in use problem based learning combined portfolio assessment of student learning outcomes was analyzed by N-Gain, independent sample t test and classical completeness. The results showed that improvement of cognitive aspects of the experimental class was higher than the control, learning outcomes of the experimental and control classes were significantly different, and the classical completeness of experimental class was more than 80%. Conclusion of the research problem based learning model with portfolio assessment applied to the immune system material is effective.