How often and how well evidence-based practices are used is measured by “fidelity,” meaning how well a practice is implemented as intended. Fidelity measures may include perceptions, such as how a teacher views a practice’s usefulness and effectiveness. For evidence-based practices to be effective, teachers need to use them as intended — in other words, with fidelity.3 However, not much research has focused on how early childhood teachers implement new practices or curricula with fidelity, despite big financial investments in improving early childhood programs across the United States. To address this issue, we explored how teacher and program characteristics, including teacher attitudes and perceptions, were related to fidelity when implementing STREAMin3, a new comprehensive curriculum for classrooms serving children ages birth to five years old. (author abstract)