This paper charts the design and application of a system to support 11-14 year old students' learning of algebraic generalisation, presenting students with the means to develop their understanding of the meaning of generality, see its power for mathematics and develop algebraic ways of thinking. We focus squarely on design, while taking account of both technical and pedagogical issues and challenges, and provide an account of how we have designed and built a system with a very close fit to our knowledge of students' difficulties with the subject matter. We report the challenges involved in building a system that is both intelligent and exploratory, a learning environment in which both student and teacher are supported without explicit tutoring. (Contains 18 figures.)