Development of a Test Instrument for Students’ Mathematical Reflective Thinking Ability on Systems of Two-Variable Linear Equations

The purpose of this study is to produce a valid, reliable, and effective mathematical reflective thinking ability test instrument on the Two-Variable Linear Equation System (SPLDV) material. The instrument was validated by three experts across material, construction, and language, with the results indicating that it is suitable for use after minor revisions based on the validators' suggestions. This study is a Research and Development (R&D) study with the ADDIE model approach (Analysis, Design, Development, Implementation, Evaluation). The analysis stage is data collection through a needs questionnaire, the design stage is planning and reviewing the design with experts, the development stage consists of needs analysis conducted by interviews and curriculum studies, question design based on reflective thinking indicators, development and validation by experts, the implementation stage is the implementation of trials with 32 10th grade students, and the evaluation stage is based on the results of the analysis by conducting formative assessments for product refinement. The results of the study indicate that all test items have been proven valid with a calculated r value greater than r table (0.349), with an instrument reliability value of 0.902, which is included in the outstanding category, and an average student score of 73, indicating that this instrument has good effectiveness. Therefore, this instrument is deemed suitable for measuring the mathematical reflective thinking ability of 10th-grade high school students in the context of two-variable linear equation systems (SPLDV).