This study was conducted in Class VII-A of SMP Negeri 1 Sinunukan during the first semester of the 2025/2026 academic year, involving 27 students as participants. The research process was carried out in two cycles, following the framework of classroom action research. Data collection was conducted through direct observation (peer assessment) by observers and self-assessment by students during the learning process. The collected data were analyzed using descriptive statistical analysis to identify patterns of improvement in students’ mathematical understanding and learning motivation. The main objective of this study was to improve students’ mathematical understanding through the implementation of the Peer Tutoring Method in the topic of arithmetic operations involving rational numbers. The success indicator of this research was the increase in the average level of students’ collaborative skills and their learning motivation across the two cycles. The findings revealed that in Cycle I, the average percentage score of students’ collaborative skills was 55.5%, while in Cycle II, there was a significant improvement with an average score of 81.4%. This increase indicates that students became more active, confident, and motivated in engaging with mathematical concepts through interaction with peers. The peer tutoring strategy fostered a supportive learning environment that enhanced students’ cognitive and affective engagement, allowing them to construct mathematical knowledge collaboratively. Therefore, it can be concluded that the application of the peer tutoring method significantly contributes to improving students’ mathematical understanding and learning motivation. The method also promotes the development of social interaction and cooperative learning skills, which are essential for achieving higher academic outcomes in mathematics.