In this study, we designed geometry learning activities so that students could apply newly learned knowledge to solve real-life problems, such as estimating the distance to real objects they find in their local community, measuring objects' length, width, and height, and calculating objects' surface area. Our participating students were divided into three groups, and each group used different tools in different contexts for the measurements and calculations: the students in control group A used traditional tools, such as rulers, paper, and pencil, and their learning activities took place in the local community; the students in control group B used traditional tools as well, but their learning activities took place in classroom; the students in the experimental group learned geometry in a local community setting using a tablet PC-based ubiquitous geometry (UG) system that we developed for this study. We tested the difference in geometry learning performance, such as geometry reasoning and spatial estimation abilities, among the three groups. We also investigated the perceptions of students in the experimental group toward the UG system. Furthermore, student behaviors toward measuring objects using the UG system and their relationship with geometry reasoning and spatial estimation abilities were explored. Our results showed that the geometry learning performance of the students in the experimental group was significantly better than that of the students in the other two groups. Our results also showed that the students in the experimental group had high learning motivation and intention to use the UG system. Further analysis revealed that the students who measured more objects in the real world using our system had better geometry reasoning and spatial estimation abilities. However, only the students who measured objects correctly had high learning gains. The results suggest that the learning activities supported by the UG system were beneficial for enhancing geometry reasoning and spatial estimation abilities because the students were able to apply newly learned knowledge to the real world. Based on the results, we give some advice on the design of learning activities.