The use of data to inform decisionmaking and practice at the school and district levels is now a common feature of reform efforts. Advances in districts' technological capacities have produced data systems that allow a flow of data to and from schools, often to the point of creating an overwhelming flood of information. To make the flow of information usable, it is critical that it is accompanied by clear decision rules on how to organize, interpret, and act on the data and the information they provide. Increasingly, schools and districts are turning to indicators to narrow the flow of data to the factors that truly matter for student success. Although, in principle anything that can be quantified can be used as an indicator, effective indicators provide a signal of a later outcome. Effective indicators can be used to identify students who are likely to achieve (or fail to achieve) an outcome, or to highlight actionable leverage points for altering that outcome. For college readiness indicators, it becomes particularly important to identify actionable leverage points because the outcome they are intended to predict--college success--occurs after the students have left high school. In other words, identifying which students are likely to complete college is only a starting point. This resource is intended to guide district administrators as they consider what indicators to include in their indicator systems and how to focus their efforts to improve students' college readiness. It describes four characteristics of effective indicators, drawing on the work of the University of Chicago Consortium on Chicago School Research (UChicago CCSR) with the Chicago Public Schools (CPS). CPS used evidence from research to guide the development of two separate indicator systems: the on-track indicator for high school graduation and the Free Application for Federal Student Aid (FAFSA) completion indicator system for college enrollment. These experiences provide valuable lessons for other districts as they develop their own college readiness indicator systems.