<![CDATA[This study aims to determine the development of a valid, practical, and effective mathematical logical thinking ability test instrument for flat geometry material for students at SMP Negeri 3 Mojoagung. This instrument is designed to objectively measure students' logical reasoning ability in solving problems related to geometric concepts of flat geometry. This research is a Research and Development (R&D) study, adapting the ADDIE (Analysis, Design, Development, Implementation, and Evaluation) model. The research procedure follows the ADDIE model development stages: Analysis, Design, Development, Implementation, and Evaluation. These stages are carried out sequentially and systematically to produce a valid, practical, and effective instrument. The results of this study indicate that the developed test instrument meets good quality criteria, namely the mathematical logical thinking ability test instrument (TKBLM) for flat geometry material is declared valid, practical, and effective. The validity of the TKBLM instrument can be seen from the TKBLM instrument validation percentage, which is 93%, categorized as very valid. The practicality of the TKBLM instrument can be seen from the percentage of the readability questionnaire, where 85% of students' results showed a ???? ≥ 75%. Meanwhile, the effectiveness of the media can be seen from the TKBLM results, where for each indicator, at least one student met the logical mathematical thinking indicator. Thus, this test instrument is suitable for use as an effective measurement tool to evaluate students' logical mathematical thinking skills in the material on plane figures. Keywords: Test Instrument, Logical Mathematical Thinking, Plane Figures.]]>
