The benefits of applying technology to education have been often questioned. Learning through digital devices might imply reducing the children’s physical interaction with the real world, when cognitive theories hold that such interaction is essential to develop abstract concepts in Mathematics or Physics. However, conflicting reports suggest that tangible interaction does not always improve engagement or learning. A central question is how cognitive theories can be successfully applied to the design of interactive systems in order to achieve enhanced learning experiences. In this paper we discuss the interaction design of a mixed-reality system for mathematics learning for school-aged children. Our design approach combines inspiration from previous frameworks with a user-centered design process with early prototype evaluations. As a result of this process we have created a mixed-reality environment for lowcost tablets and an augmented version of the Cuisenaire rods, a milestone of the manipulatives for mathematics learning.