The broad stair is an example of how Dr Montessori isolated abstract concepts such as size, colour, and shape in the materials she developed so that the young child could explore, classify and categorize. The Broad Stair is used to explore size. Only height and breadth changes. No other quality changes. In the stair there are 10 prisms, which the child builds into a ‘stair’ from broadest to narrowest or uses to build in different ways as he explores the concepts inherent in the material.