Abstract
This study aims to examine the effect of the Problem Based Learning (PBL) learning model on the learning interest and mathematics learning outcomes of fifth grade elementary school students, especially on the addition and subtraction of fractions. The background of this research problem is the low enthusiasm and learning outcomes of students in three elementary schools in Dua Koto District, Pasaman Regency, which is caused by conventional, teacher-centered, and less contextual learning methods, so that only 43–64% of students achieve learning mastery. This study uses a quantitative method with a quasi-experimental design in the form of a non-equivalent control group design. The research sample consisted of 39 students divided into an experimental class (PBL) at SDN 05 Tonang Raya (n=17) and a control class (Expository) at SDN 21 Kelabu (n=22). The instruments used include a learning interest questionnaire (reliability 0.875) and a learning outcome test (reliability 0.849) that have been validated by experts and tested. Inferential data analysis was performed using t-tests and F-tests after the data were declared normal and homogeneous. The results showed that the PBL model was significantly more effective than the expository model. Hypothesis testing revealed a positive effect of PBL on student learning interest, with a significance value of 0.031 (<0.05), indicated by an increase in the percentage of students in the very high category from 23.5% to 82.4% in the experimental class. PBL also had a positive effect on student learning outcomes, with a significance value of 0.016 (<0.05), as evidenced by the experimental class's posttest average (83.29), which was significantly higher than that of the control class (71.50). Furthermore, there was a significant interaction between learning interest and learning outcomes (Sig. 0.006 <0.05). The conclusion of this study is that PBL has been proven to be holistic in enhancing students' affective and cognitive aspects, making it an effective alternative learning strategy for improving the quality of mathematics learning in elementary schools