Start out by working with the cylinder blocks. The cylinder blocks are sets of blocks with various sizes of cylinder. One set has cylinders that vary by height, length and width. Each cylinder fits in a single hole in a large wooden block. Children may remove all cylinders to compare them, play with the cylinders outside of the blocks or enjoy lining them up in various formations inside and outside of their blocks. As they do, they will begin to compare and contrast different dimensions.
Build a tower using the cubes lesson--also called the pink tower lesson. This lesson consists of ten solid wooden cubes. They can be stacked with the largest on the bottom and the smallest on the top to form a tower. In order to succeed at building the tower, the child must be able to compare the cubes in order to place them in order from largest to smallest.
Introduce the vocabulary terms "largest" and "smallest." Ask the child to point at the largest cube or the largest cylindar, depending on the lesson. Then ask him to identify the smallest. You can use all ten of any object for this exercise, or just remove two or three and ask the child to select between them.
Create a stairway using the Montessori broad stair lesson, also called the prisms lesson in some schools. The broad stair lesson consists of ten wooden rectangles that are all the same length but that are different heights and widths. The tallest is also the broadest, and the shortest the thinnest. They can be arranged from tallest to shortest or broadest to narrowest to create a "stairway." This lesson should be used only after a child is quite comfortable with the cylinder blocks and the pink tower, as this lesson requires children to compare two factors (height and width) instead of just size.
Introduce the vocabulary terms "wider" and "narrower" as well as "tallest" and "shortest." Do not do this until the child is very comfortable building the broad stair. Then, you can ask her to identify the tallest and the shortest blocks as well as deciding which of two blocks is wider or narrower.