Debate over the design of state and federal accountability systems is an important ongoing issue for policy makers. As we move toward next-generation accountability through No Child Left Behind's (NCLB) waivers and reauthorization drafts, it is important to understand the implementation and effects of key elements of prior accountability systems. In this policy brief, we investigate an under-researched feature of NCLB accountability—the use of safe harbor to meet proficiency rate objectives. We use school-level data on California schools between 2005 and 2011 to investigate the prevalence of safe harbor over time. We find dramatic increases in recent years, primarily for the objectives for historically disadvantaged groups. Furthermore, we find no evidence that schools using safe harbor meaningfully outperform schools failing Adequate Yearly Progress in the short or long run, casting doubt on the utility of the measure. We conclude with recommendations to policy makers, including state assessment and accountability coordinators, regarding accountability policy design in future laws.