<![CDATA[Mathematics learning is an important part of basic education because it functions as a foundation for understanding various scientific concepts. This study aims to improve second-grade students' learning outcomes in recognizing whole numbers through the application of the Problem Based Learning (PBL) model. The research employed the Classroom Action Research (CAR) method based on the Kemmis and McTaggart model, comprising four stages: planning, action implementation, observation, and reflection, and was conducted over two cycles with 20 second grade students at SDN Cintajaya as subjects. Data were collected through learning outcome tests, observation sheets on lesson-plan quality and on teacher and student activities, and documentation, then analyzed using both quantitative and qualitative approaches. The results indicate that the percentage of students reaching mastery increased from 40% (average score 64.55) before the action, to 60% (average score 73.75) in Cycle I, and to 85% (average score 84.75) in Cycle II, thereby meeting the study's success indicator of at least 75% mastery. The quality of lesson planning improved from an average of 3.58 to 3.75 (a 4.75% increase), while the implementation of learning activities improved from 3.30 to 3.57 (an 8.18% increase). Thus, the Problem Based Learning model is proven to enhance student learning outcomes in recognizing, sequencing, and comparing whole numbers among second-grade students at SDN Cintajaya.]]>
