Nationwide, a growing percentage of kindergarten through grade 12 (K-12) teachers report regularly using standards-aligned English language arts and math curriculum materials. Despite this uptick in the regular usage of standards-aligned materials across the United States, not all teachers use these materials for the majority of their instructional time, even when the materials are required or recommended by their districts. For education leaders who hope to use curriculum materials as levers for improving instruction, adopting standards-aligned materials is only the first step. Encouraging teachers to use these materials with integrity remains a challenge. In this report, the authors use results from the 2023 American Instructional Resources Survey to explore whether teachers feel that the curriculum materials required or recommended by their schools or districts are appropriately challenging for their students.