Monarch larvae grow dramatically over two to three weeks. After data collection, growth in size is quantified and change in appearance (shape and features) is described. Amounts of growth can vary by individual and over the larval stages, even for one individual. Students learn to coordinate the amount grown with the time intervals between measurements, and calculate rate. Studying growth rate allows students to compare growth in the early stages to growth in later ones. They learn about patterns in growth rates by using line graphs that are also useful in many other contexts.

Initially, children describe growth in qualitative terms, "It gets bigger." Through measuring the monarch larvae, recording data for length and width, creating line graphs, and calculating growth rates, students develop quantitative understanding of growth and growth rates. They also learn features and uses of representational tools, such as graphs, that can be used more generally when addressing questions of change over time.