eng Science and Education Publishing American Journal of Educational Research 2327-6150 2018-12-06 6 11 1589 1592 10.12691/education-6-11-20 EDUCATION201861120 article Sri Wulandari sriayubintanglestari@gmail.com 1 Amin Fauzi 1 Wamington Rajagukguk 1 Postgraduate Program in Mathematics Education, Medan State University, Medan, Indonesia This study aims to describe: 1) the validity, practicality and effectiveness of the teaching materials developed, 2) describe the improvement of students' mathematical reasoning abilities using the developed teaching material. The development of teaching materials based on the metacognition approach uses a 4-D model developed by Thiagarajan, Semmel and Semmel. The subjects in this study were students of class VIII-8 and VIII-9 SMP Negeri 17 Medan. From the results of field trials I and field trials II obtained: 1) teaching materials that meet valid, practical and effective criteria, 2) there is an increase in mathematical reasoning abilities. http://pubs.sciepub.com/education/6/11/20/education-6-11-20.pdf teaching materials metacognition approach 4-D development model mathematical reasoning ability