The choice of appropriate educational materials, visual or physical, for teaching mathematics to children on the autism spectrum, is an important topic in the context of inclusive education. In this article we first focus on some theoretical issues concerning the manipulative material, on the teaching of proportional quantities in the Greek high school and the difficulties it presents, as well as on the Asperger syndrome. We present the design, the implementation and the basic results of a teaching intervention conducted in a 14-year-old student with Asperger syndrome studying in the 8<sup>th</sup> grade of a high school in Greece on the use of manipulative materials for solving authentic real-world and word mathematical problems. The research showed that the student understood the differences between the real analogy and the illusion of linearity inherent in the problems he was given to solve using manipulatives. The paper concludes with suggestions, perspectives and limitations for teaching proportion problems and the tackle of the illusion of proportionality using manipulatives.