Innovative learning technologies and modernizing the education system can improve education. In the last decade, the use of Augmented Reality (AR) has increased rapidly, especially in the education sector. However, only limited articles have reviewed the stages of developing and applying AR material for learning mathematics. As AR is still considered a relatively new tech-nology in educational fields, there is a natural need for research-based guidelines to design effective and applicable AR tools for school-based learning. The main purpose of this study is to design, develop and reveal the effect of an AR material to improve spatial ability in secondary school students using mobile devices. For this purpose, an AR material that focuses on the change of the surface area of the cube in case of removing cubes from different parts of the cube was developed within the framework of the Waterfall Model and the effect of this material was examined. In this research, in which case study methodology was adopted, data were collected through achievement tests, questionnaires, and interviews. The results showed that students were generally able to accept using AR to learn geometry and AR-supported teaching methods significantly improved students' learning outcomes.