This lesson is optional because it reviews concepts learned in prior grades. If students understand how to describe distribution shapes as well as the meaning of mean, median, and standard deviation, this lesson may be skipped.

The mathematical purpose of this lesson is to interpret the standard deviation as a measure of variability and to describe the shapes and properties of distributions. The properties of bell-shaped distributions are a particular focus. Although it is rare to have perfectly bell-shaped distributions in reality, approximately bell-shaped distributions can be modeled by a normal curve, which will be the focus of the next several lessons. When students articulate things they notice about a dot plot, students must attend to precision in the language they use to describe what they see (MP6). When students trade roles explaining their thinking and listening about the shape of a distribution and summary statistics for a dot plot, they are explaining their reasoning and critiquing the reasoning of others (MP3).