This study contributes to the field by identifying a broad range of traditional and newer middle grade policies and practices, and determining in California which of these differentiate higher- from lower-performing schools serving similar student populations, with performance measured by the state's standards-based tests. Based on a sample of 303 middle grade schools located across California, the research team conducted three large-scale surveys: of middle grade principals; of English language arts and mathematics teachers; and of many of these schools' district superintendents. This study shows that, although the socioeconomic backgrounds of students are one strong predictor of school-level academic achievement, the practices and policies enacted by middle grade educators also have a significant relationship with these outcomes. Their focus on their middle grade mission, and the resources they have available to pursue their goals, can make a difference. The interrelated practices identified in this study may help middle grade schools and districts--in California and nationally--continue their efforts to improve students' academic outcomes at a critical time in their academic careers. (Contains 6 figures and 1 footnote.) [For this report's narrative summary, see ED508674. For its appendices, see ED508675 (Appendix A), ED508678 (Appendix B), ED508677 (Appendix C), and ED508676 (Appendix D).]