Program exposure is a key element of implementation fidelity and refers to the amount of an intervention received by participants. For students using IXL, setting a target program exposure (i.e., an IXL usage goal) both allows monitoring of implementation fidelity and enhances students' motivational and learning outcomes. IXL's proposed optimal usage guideline for students to strive to reach proficiency in at least two skills per week (2 SP/week) is based on a comprehensive analysis of various usage levels and associated outcomes (An, 2021a). This 2 SP/week implementation and usage goal encompasses a number of important characteristics (e.g., specificity, proximity, and appropriate difficulty) that are tied to achieving better learning outcomes as suggested by the literature. This document provides an overview of the theoretical background for setting this specific usage goal and summarizes the empirical evidence for the added value of reaching proficiency in at least two skills per week over typical IXL usage.