Data-based decision making has been the mantra of the school reform movement since the late 1980s, but California does not yet have an effective system for collecting and using vital school information. Cali-fornia has taken a number of steps to address this shortcoming. These include the Public School Account-ability Act of 1999 and Senate bills 1453 and 1614, which improve California’s education data system by establishing student and teacher tracking mechanisms. Despite these efforts, California continues to lag behind other states in data collec-tion and management, in policy evaluation and data use, and in funding for local school districts to support the collection and main-tenance of reliable education data. This brief highlights the elements of an effective data system, with a particular focus on issues related to data collection. The authors show that valuable lessons can be learned from the high quality data systems that have been created in other states, and in organizations in both the public and private sectors. They argue that data, if used wisely, can help to transform California’s education system.