Nowadays the educational community agrees on improving student’s achievement in mathematics. This is one of the most complex and less successful subjects along the school years. Research focused on the development of mathematical competence highlighted how much important an early intervention is for further achievement. Likewise, our education system is immersed in a continuous change, in a certain way, due to the influence of technological development and the impact on our lives. Therefore, in order to facilitate learning, students’ environment should be brought closer to mathematics. A way of approaching them would be using mobile devices to train school competences and learning factors. The present study introduces one of the applications (APPs) designed for tablets and smartphones adapted to different operating systems. This APP was designed and developed to improve number sense. It is focused in early pre- and primary school students. The APPs are shown as an innovative and entertaining tool, which aims to contribute the improvement of number sense in students in their transition from Nursery to Primary Education. The APP was designed for training “subitizing”, that is, the ability to establish the cardinality of a number set without counting. The APP’s design is based on numerical learning’s cognitive models. It also provides benefits by the use of tablets and Smartphones as mediating learning tools and positive reinforcement. The main objective of this study was to contribute to learning number sense and successfully achieve requirements in school and math topics in everyday life.