In school mathematics, representations of solid figures and three-dimensional geometric objects generally rely on two-dimensional projective representation modes on students' textbooks. In learning environments, these representation modes create a kind of cognitive filter, which prevents students with low spatial ability to comprehend and envision three-dimensional objects. Studies showed that spatial ability could be improved by means of suitable concrete models and computer created models in learning settings. Thus, fostering students' spatial ability helps to overcome and eliminate negative effects of this cognitive filter. However, some studies suggest that this cognitive filter may even occur while working with computer created objects since computers generally rely on two-dimensional digitizer panels on screen technology. On the other hand, augmented reality interface allows a new way of learning environment which could help to overcome this cognitive filter by providing unique representation modes and opportunities to foster students' spatial ability. In this study, an intervention with an augmented reality interface to foster students' spatial understandings were reported in terms students' invented strategies for spatial concepts. In this sense, eight seventh graders worked on spatial tasks with an augmented reality interface in learning settings. Findings revealed that while proceeding on spatial tasks, students could invent, use and modify spatial strategies. Moreover, students' spatial understanding was fostered as they progressed on tasks with the designed augmented reality interface. This study is a part of an educational design research which was focused on design and development a proper augmented reality tool to foster spatial ability of students. As a result of this study, with the help of combination of augmented reality interface and spatial tasks, teachers will be provided with a new tool to visualize mathematical concepts and students could be supported with this new tool as a new learning material.