Differentiated instruction, standards-based curriculum, and end of course assessments (ECAs) are not mandated in most high schools across the United States. As such, classroom grades do not accurately reflect district report cards. In particular, grades at the study site, a suburban high school, do not show the specific standards and benchmarks students have mastered, nor those still needing addressed. The purpose of this study was to examine the impact of differentiation and standards-based curriculums on common ECAs at the high school. This quasi-experimental study with between-group comparative design addressed whether students in differentiated classrooms that utilized standards-based curriculums scored higher on ECAs than did those in traditional (nondifferentiated) classrooms. The theoretical basis for this study was the theory of differentiation, or modifying instruction to meet the needs of all learners. Independent-samples t tests found no statistically significant differences between mean ECA scores of students in differentiated/GLI classrooms and students in traditional classrooms. This study may influence social change by contributing to the discussion of standards-based assessments, standards-based curriculums, and standards-based reporting for all subjects in Grades 6-12. In so doing, schools and districts can better use their district report card to help understand their adequate yearly progress (AYP). The results suggest additional research into the potential impact of differentiated curriculums on subgroup populations such as gender or race.