Teachers must provide high-quality instruction based on evidence-based practices to provide students meaningful opportunities to learn and to improve school outcomes. Although teachers have access to a variety of resources on evidence-based practices, poor implementation may limit the effectiveness of teacher practices, as indicated by low levels of student achievement and flat rates of progress. However, inadequate student response to instruction or intervention may also be due to a mismatch between teacher practices and student needs such as when students require more intensive support. As a result, school teams must determine the degree to which teachers provide instruction and intervention as intended (i.e., fidelity of implementation) to determine if an inadequate student response is due to poor implementation of practices that match student needs or due to a need for more intensive support. The authors report the necessity of including contingencies for measuring fidelity within school-wide assessment practices. Methods for assessing fidelity that can be used by school administrators, school psychologists, and teachers are discussed. Examples of recommended methods are provided for both academic and behavioral practices.