At KIPP Comienza Community Prep--an elementary school in Huntington Park, California, where 94 percent of students qualify for free lunch, and more than 60 percent are English language learners--most kindergarteners start out well below pre-reading levels. In 2015, however, just a few years after these students walked in the school doors unable to identify the letters of the alphabet, 81 percent met or exceeded standards in English on the Common Core--aligned Smarter Balanced Assessment Consortium (SBAC) assessment; 82 percent did so in math. Principal Shirley Appleman attributes her school's success in shifting to college- and career-ready standards to the robust use of data. Using data at this level of consistency and rigor--so that it informs instruction every day, in every classroom--requires substantial planning and organization. This case study describes several practices that Appleman and her team maintain to ensure that student data drives every decision about instruction and curriculum at KIPP Comienza. Questions for reflection conclude the study. [For the main report, "Ambitious Leadership: How Principals Lead Schools to College and Career Readiness," see ED584804.]