<![CDATA[This study aims to describe the implementation of the Problem Based Learning (PBL) model in mathematics learning for first-grade students at State Elementary School I Wonoharjo, Wonogiri Regency. This study employed a qualitative approach with a descriptive method. Data were collected through observation, interviews, and documentation. The research subjects consisted of the first-grade teacher and students. The results showed that the implementation of the Problem Based Learning (PBL) model was carried out through the stages of preparation, implementation, and assessment. At the preparation stage, the teacher prepared the teaching module, teaching materials, learning media, PBL model, and Student Worksheets (LKPD). The learning implementation consisted of preliminary, core, and closing activities. In the core activities, five stages of PBL were implemented: orienting students to the problem, organizing students for learning, guiding individual and group investigations, developing and presenting problem-solving results, and analyzing and evaluating the problem-solving process. Assessment was conducted through diagnostic and formative assessments. The implementation of PBL provided opportunities for students to actively understand and solve mathematical problems, collaborate with peers, express their opinions, and reflect on the learning process. The teacher acted as a facilitator and provided guidance according to the characteristics of first-grade students, who still required assistance in understanding and solving problems. Keywords: Problem Based Learning (PBL), mathematics instruction, first-grade students, elementary school]]>
