Developing Ethnomathematical-Based Learning Stages on Mathematical Communication Skills with Kastolan Error Analysis

Ethnomathematics-based learning has been effective for students' mathematical communication skills but can still be optimized again by minimizing mistakes that students often make. So the objectives of this study are: 1) to analyze student errors in solving mathematical communication problems in terms of student ability categories; 2) analyze the Ethnomathematics-based learning process with the help of the Geogebra application; 3) develop Ethnomathematics-based learning steps based on student error analysis. The study subjects were randomly selected, namely 36 students of junior high school class IX odd semester academic year 2023/2024 SMP Negeri 1 Tanara. Data were obtained from mathematical communication skills tests, interest questionnaires, observation sheets, and interview sheets. Data analysis techniques start with data analysis, tests of students' mathematical communication skills with qualitative data analysis, then to interpret research findings, followed by quantitative data analysis. The analysis of students' errors in solving mathematical communication problems in terms of student ability categories found that students in medium and low ability categories made more procedural errors. At the same time, students in the high-ability category tend not to make significant mistakes. The results of the triangulation found two stages of learning needed to minimize student errors, namely the exercise stage and the investigation stage. The stages of Ethnothematics-based learning consist of exploration, mapping, explanation, exercise, investigation, and reflection. The effectiveness of the learning model developed on students' mathematical communication skills will be analyzed for further research