<![CDATA[This study aims to identify the types and causes of errors made by ninth-grade high-achieving students at SMP Yapis Manokwari in solving Systems of Linear Equations in Two Variables (SPLDV) problems based on Kastolan’s Theory. This research employed a descriptive qualitative approach. The research subjects were selected using a purposive sampling technique. Data were collected through written tests, semi-structured interviews, and documentation. The research instruments consisted of SPLDV test items and interview guidelines that had been validated by two Mathematics Education lecturers. The data were analyzed using the Miles and Huberman model, which includes data reduction, data display, and conclusion drawing. The results showed that high-achieving students still made conceptual, procedural, and technical errors in solving SPLDV problems. Conceptual errors were indicated by students’ inability to translate word problems into appropriate mathematical models. Procedural errors were reflected in the incorrect application of solution steps and the failure to complete the solution process. Technical errors were identified through mistakes in arithmetic operations. The causes of these errors included internal factors, such as a lack of conceptual understanding, weak computational skills, low accuracy, and forgetting solution procedures, as well as external factors, including poor study habits, lack of material review, teaching methods, and an unconducive learning environment. In conclusion, high-achieving students are still prone to making errors in solving SPLDV problems despite having good academic performance. Keyword : Student Errors, SPLDV, Kastolan Theory, High-Achieving Students]]>
