The purposes of this study are to investigate the effects of an augmented reality application on students' spatial ability and academic achievement, and to analyze the opinions of students and their teacher concerning augmented reality environments. To collect quantitative data, a quasi-experimental pretest-posttest with a control group design was employed, and to collect qualitative data, a case study design was used. The study was designed around the lesson topic "geometric objects and measuring volume," and 88 sixth grade students participated. While the students in the experimental group studied the lesson topic using augmented reality and real objects, the students in the control group used only real objects. The results indicate that though a significant increase was observed in the spatial ability of both groups, no significant difference was found between the post-test spatial ability mean scores of the experimental and control groups. In addition to the spatial ability results, the students' academic achievement scores in the experimental group significantly increased, but the small increase in the control group students' scores was not significant. No significant difference was found between the post-test academic achievement scores of the experimental and control groups. In addition to the quantitative data, the qualitative data gathered from the students and the teacher yielded valuable information that may assist researchers who attempt to integrate augmented reality in education.