Part of the Stanford Center for Opportunity Policy in Education (SCOPE) research series titled "Teachers' Time: Collaborating for Learning, Teaching, and Leading," this case study looks at Hillsdale High School, a large, comprehensive high school located in San Mateo, California, a high-tech enclave of Silicon Valley nestled 23 miles south of San Francisco and 32 miles north of San Jose. The San Francisco Peninsula is famous for high housing costs and serving families with high educational attainment, given its close proximity to Silicon Valley. The students at Hillsdale come from the surrounding neighborhoods of San Mateo and Foster City and reflect the full socioeconomic and cultural diversity of San Mateo County. Hillsdale allocates time in service of very specific and intentional goals: (1) to personalize learning for students; (2) to support collaboration among teachers; and (3) to develop rigorous, cross-disciplinary units of study for stu­dents. Thus, time, at Hillsdale, is used to foster learning and development for both students and teachers. The data for this case study were gathered as part of a larger study of four public schools across the United States that organized teacher time and work in innovative ways. [For the cross-case study, "Teachers' Time: Collaborating for Learning, Teaching, and Leading. Time Matters: Teacher Collaboration for Learning and Leading," see ED591145. For the Research Brief, see ED591147.]