Reconfigurable modular robots (RMRobots) can change their shape and functionality (e.g., locomotion styles) to fit different environments, and have been widely investigated in applications, such as exploration and inspection. In this paper, we present a new application of RMRobots for improving human spatial ability which plays a significant role in developing an individual's performance and achievement in science, technology, engineering, and mathematics (STEM). Two user studies are conducted, and the results show that: 1) the task performance of interacting with RMRobots has a significant positive relationship with mental rotation, a widely used measure of spatial ability; and 2) interacting with RMRobots can effectively improve the performance on a task related to spatial reasoning skills according to behavioral data and electroencephalograph (EEG) indices. Our presented study broadens RMRobot research in the area of human-robot interaction.