Curriculum-based measurement (CBM) is a system of assessment used to screen for students at risk for poor learning. CBM benchmark screening assessments are typically administered to all students in the fall, winter, and spring, and these data are frequently used by researchers to model and perhaps explain within-year growth. Modeling growth with three time points involves distinct choices in the functional form of growth that can be modeled as well as the parameters that can be estimated. Generally, only a linear growth model can be fully specified; however, research suggests that within-year CBM growth is often nonlinear, with decreasing or decelerating growth across the year. The purpose of this brief is to demonstrate how an estimated slope factor loading approach can be used in a structural equation modeling (SEM) framework to obtain a direct statistical test of nonlinearity provided by the output of your SEM program.