Recent studies have brought attention to the pedagogical potential of mobile devices, and various experiments have tested tools in handheld devices, indicating that they strengthen and support learning in different fields. The purpose of the work presented in this paper was to design a 3D construction mobile game for 3D spatial visualization training, with the aim of familiarizing users with a 3D environment and improving their understanding of the 2D-3D relationship. This paper describes the architecture of the system that we developed, which includes several different applications: (a) a mobile game played on touch screen devices to permit students to solve exercises about building models with unit-sized cubes in a 3D environment, (b) a PC application, to permit the teacher to design exercises and manage users, and (c) a server application and a database to collect and manage data. The J2ME Mobile 3D Graphics library is used and development is done in Netbeans. Satisfaction questionnaires and observation records were kept of work done by the users in order to evaluate the mobile game. The results show a high degree of satisfaction with the game and that users realize how useful this game can be for the proposed aims.