<![CDATA[Abstract This study aims to develop teaching materials for flat shapes using a realistic mathematics education approach to teach students' mathematical problem solving skills and to determine the quality of teaching materials in terms of validity, practicality, and effectiveness. This research is a development research with the ADDIE development model (Analysis, Design, Development, Implementation, and Evaluation). The subjects in this study were 28 grade VIII students of SMP Negeri 7 Padang Sidempuan. The research instrument used to measure the quality of teaching materials was in the form of expert validation questionnaires, student response questionnaires and post-test results of students' mathematical problem solving abilities. The expert validation questionnaire was used to measure the validity of the teaching materials while the student response questionnaire was used to measure the practicality of the teaching materials and the post-test results of students' mathematical solving abilities were used to measure the effectiveness of the class VIII students' teaching materials at SMP Negeri 7 Padang Sidempuan. The results of this study indicate that the quality of teaching materials is seen from the validation assessment of material experts with an average score of 75.5%, for the assessment of media experts with an average score of 78.33%, and for the assessment of linguists with an average score amounted to 90.67% with each score included in the eligible criteria. The overall results of the expert's assessment show that the teaching materials developed have "good" (decent) criteria based on the assessment by 6 experts with a percentage score of 81.5% in the "very valid" criteria. And the results of the questionnaire responses of students to teaching materials seen from the aspect of practicality with a percentage score of 92.78% in the "very practical" criteria and the post-test results of students' mathematical solving abilities seen from the aspect of effectiveness with an average score of 74.46 in the category " effective. So it can be concluded that the overall results of the study indicate that the teaching materials of flat shapes with a realistic mathematical approach to teach students' mathematical problem solving skills are valid, practical, effective and suitable to be used as learning tools. Keywords: Teaching Materials, Problem Solving Ability, Realistic Mathematics Education Approach]]>
