Background/Context: A central aim of standards-based reform is to close achievement gaps by raising academic standards for all students. Rigorous standards coupled with aligned assessments will purportedly improve student opportunity to learn through high-quality, aligned instruction. After 10 years of No Child Left Behind (NCLB), the impact of standards-based reform on student achievement in English Language Arts (ELA) remains questionable. Improving ELA achievement has been a central focus of NCLB, so this study examines changes in the cognitive demand coverage of teachers' ELA instruction over time during the NCLB era. Research Question: Three research questions guide the analyses: (a) How have the cognitive demand levels of ELA instruction changed over time? (b) To what extent have changes in the cognitive demand level of ELA instruction differed across settings based on school and classroom characteristics? (c) How have cognitive demand levels changed as school composition has changed? Subjects: The sample consists of 2,064 ELA teachers in grades K-12. The teachers come from 344 schools in 15 states; the majority are K-3 educators. Research Design: This study relies on secondary data analysis of teachers' responses to the Surveys of Enacted Curriculum (SEC). First, we used a within-teacher fixed-effects regression model to determine how cognitive demand coverage changed over time. Second, we examined how these changes varied by school and classroom characteristics (e.g., Title 1 status). Finally, we investigated how changes in cognitive demand coverage varied based on within-school changes in school and classroom characteristics. Findings: Findings demonstrate that cognitive demand coverage has changed considerably over the study period, moving from higher and lower levels toward the middle. There were, however, notable variations between schools serving different populations of students. Schools in urban areas serving predominantly students from historically marginalized groups (e.g., racial/ethnic minorities) saw more of a shift toward lower levels of cognitive demand than was seen at schools serving whiter and wealthier students. Conclusions/Recommendations: There have been different instructional responses to standards and assessments in different settings, with decreased cognitive demand in urban/high-needs schools relative to suburban/lower-needs schools. These shifts seem to run contrary to the idea that all students should be held to the same high standards. We recommend that future research consider longitudinal data regarding teachers' instruction. It is also important that policymakers, particularly those working on the Common Core State Standards, consider these differential responses to standards-based reform.