This paper describes a 3-year evaluation of Core Knowledge Sequence implementation in 12 schools nationwide. The Core Knowledge Sequence, a whole-school curricular reform model, provides a planned progression of specific topics to teach in language arts, history, geography, math, science, and fine arts for grades 4-6. The evaluation determined conditions under which Core Knowledge would achieve reasonably full implementation and the effects of Core Knowledge implementation in various contexts. Evaluation involved longitudinal case studies of schools (site visits, interviews, focus groups, observations, and teacher surveys). First and third graders in intervention and comparison schools completed basic skills and core knowledge testing at the beginning and end of the study. After 3 years, all 12 schools were still implementing the Core Knowledge Sequence, though only 10 authentically, and 9 had reached moderate or high implementation levels. Multilevel support for change was necessary for success. Implementing Core Knowledge helped make instruction more interesting and content-rich, provided curricular coherence, and helped increase teacher collaboration and professionalism. Core Knowledge effect sizes for all Core Knowledge test outcomes were large and educationally meaningful. When schools implemented the sequence with greater reliability and consistency, students achieved improved outcomes on all tests. (Contains 51 references.) (SM)