In today's digital age, it is widely accepted that effective use of data is essential to improving just about anything, and increasing college and career success is no exception. Yet, despite its proliferation, student information remains surprisingly underutilized, even in efforts to ease the critical transition from high school to college. This report is part of a series that encourages high schools and higher education to share responsibility for improving college completion rates by co-designing, co-delivering, and co-validating supportive experiences for all 12th-grade students through the first year of college, especially those who so often struggle in this period. An overriding question this report addresses is how to realize the largely untapped potential of K-12 and higher education systems to use data more effectively to help ease student transitions to college. This and other questions are explored using cooperative strategies that high schools and colleges can employ to use data to inform the closer collaboration needed to promote postsecondary readiness and success. The report is presented in three sections. The first section summarizes the case for school-college partnerships to lead this work. The second identifies essential elements of collaboration that secondary and postsecondary institutions should keep in mind and highlights promising practices from the field. The third addresses the challenges of creating and sustaining data collaborations between K-12 and higher education systems and recommends specific steps that each can take to establish and maintain meaningful partnerships. Endnotes are included.