This learning progression is a focused on functions in high school mathematics classroom. The many ways functions can be taught, how discrete this concept is, and the understanding that this is a concept that will continue to show up in all respective classes. There are five levels of functions that are taught at the high school level: Introduction, interpreting functions, building functions, linear, quadratic, and exponential models, and trigonometric function. Functions describe situations where one quantity determines another. Functions usually have numerical inputs and outputs and are often defined by an algebraic expression. In the progression of Interpreting Functions students learn how to understand the concept of a function and use function notation, they interpret functions that arise in applications in terms of the context, and they learn how to analyze functions using different representations.