This document describes the model used to measure student growth for institutional accountability in New York State for the 2018/19 school year and how three years of student growth results were combined to generate a three-year growth measure called the Growth Index. The Growth Index was first used in 2017/18 to make accountability determinations. The results presented in this report are based on the 2018/19 student growth model and Growth Index results, with some comparison to prior-year results. This technical report contains four sections: (1) Data -- Description of the data used to implement the student growth model, including data processing rules and relevant issues that arose during processing; (2) Model -- Description of the unadjusted statistical model; (3) Reporting -- Description of reporting metrics; and (4) Results -- Overview of key model results aimed at providing information on model quality and characteristics. [For the 2017/18, see ED601254.]