The brain is primarily designed to process sensory information about the world and produce a motor response. It’s good at that – just think of a gibbon judging which branch to leap on. What it is less good at is abstracting, that is, forming general concepts. Think of the concept ‘six’. Understanding what ‘six’ means is a giddy task for the brain. It requires exposure to many different situations, tied together by language. When all of these diverse situations can be connected conceptually, one has mastered an abstract idea of ‘six’. Astonishing really, that most children have accomplished this by the time they start school. This chapter, which also introduces key concepts about memory, demonstrates how difficult abstract thought is for the brain. It shows how the greatest challenge it faces – and where it needs the most support – is applying its abstractions to new situations. That is, most of what goes on in classrooms.