Augmented reality (AR) sandboxes are useful tools in helping students develop a three-dimensional understanding of topographic maps and landforms. Research on the AR sandbox indicates that students enjoy it, but evidence about student learning gains is inconclusive. This study aims to understand how students engage with these tools as a precedent to understanding learning gains. Technology in the form of skin biosensors allows researchers to measure skin conductance (or electrodermal activity -- EDA) as a proxy for student engagement. This study used wrist biosensors to monitor the engagement of students exposed to different instructional treatments of an AR sandbox in an introductory lab course. The data were supplemented by dynamic video of the students interacting with the sandbox. Statistical analysis of the EDA data suggests that the use of an AR sandbox, particularly during structured lab activities, increases student engagement. Regression modeling supports a relationship between spatial reasoning skills. Based on video data, students' collaborative and social interactions also showed a significant relationship with EDA. These results suggest that instructors focus on developing and using structured and collaborative activities when incorporating AR sandboxes in their courses in order to best engage students.