Public preschool programs often require the use of a research-based curriculum, yet limited research examines whether curricular decisions influence classroom processes and children's school readiness. This study uses three large samples of preschool children to examine differences in classroom quality and activities, in children's school readiness by curricular status (packaged curriculum vs. not), and across curricular packages. There were no significant differences in children's outcomes between classrooms that do and do not use a curriculum. Some significant differences existed in classroom activities across classrooms using different curricular packages; however, there exists substantial variability across classrooms implementing the same curricular package. Overall we find very little differences between preschool curricular packages for children's school readiness or classroom practices. (author abstract)