Journal of Didactic Mathematics 2023, 4(3), 200-213 Doi: 10.34007/jdm.v4i3.2073 https://mahesainstitute.web.id/ojs2/index.php/jdm journalofdidacticmathematics@gmail.com Journal of Didactic Mathematics 200 Optimizing students’ mathematical problem-solving abilities through geoboard-assisted didactic design on triangular number pattern material Muhamad Galang Isnawan* Universitas Nahdlatul Wathan Mataram, Mataram, West Nusa Tenggara, Indonesia, 83126 Sudirman Universitas Terbuka, Tangerang Selatan, Banten, Indonesia, 15418 I Ketut Sukarma Universitas Pendidikan Mandalika, Mataram, Indonesia, 83125 Fitry Wahyuni Akademi Perniagaan dan Perusahaan APIPSU, Medan, Indonesia, 20123 Naif Mastoor Alsulami University of Jeddah, Jeddah, Saudi Arabia, 23218 *Corresponding Author: galangisna19@gmail.com Abstract. The research aimed to optimize students’ mathematical solving abilities through the implementation of a didactic design developed based on lesson study activities on triangular number patterns. The research design used was didactical design research. Participants in the study were 10 students (12–15 years old) at a junior high school in Mataram, Indonesia. The researcher was the main instrument, with several additional instruments, one of which was the didactic hypothesis design. The data were analyzed using qualitative analysis. The research results revealed an increase in students’ mathematical problem-solving abilities during the implementation of didactic design on triangular number pattern material. However, the increase that occurred was less than optimal. This increase resulted from the didactic design encouraging students to use Quizizz, geoboards, and inspirational videos to solve problems. However, when watching inspirational videos and Quizizz, there were problems, such as an unstable internet connection, so activities that should have been done in groups were done collectively for one class. Article History: Received: November 18, 2023 Revised: December 02, 2023 Accepted: December 31, 2023 Keywords: Didactic design; mathematical problem- solving abilities; triangular number patterns; lesson study; didactical design research Citation: Isnawan, M. G., Sudirman, S., Sukarma, I. K., Wahyuni, F., & Alsulami, N. M. (2023). Optimizing students’ mathematical problem-solving abilities through geoboard-assisted didactic design on triangular number pattern material. Journal of Didactic Mathematics, 4(3), 200-213. Doi: 10.34007/jdm.v4i3.2073 INTRODUCTION Number patterns are one of the mathematical concepts studied in school (Risdiyanti & Prahmana, 2020). One example of the number pattern concept studied is the triangular number pattern. As one of the concepts studied at school, triangular number patterns actually become a problem for students (Wabang et al., 2023). Likewise with problem-solving abilities (Wahyuni et al., 2023). In fact, triangular number patterns have quite a role, both in other scientific disciplines and in mathematics itself (Garge & Shirali, 2012; Ulness, 2022). For example, in the engineering field, the concept of triangular number patterns is used as a tool to build triangular structures on bridge frames. Quite a lot of research has studied triangular number patterns, but not many have tried to study how to optimize mathematical problem-solving competence through lesson study activities based on didactical design research. In fact, problem-solving ability is one of the standard