Current classroom practices in the U.S. and internationally have largely been shaped by changing student demographics and accountability policies. This special issue includes manuscripts that develop conceptual frameworks or report on empirical studies addressing large-scale interventions of educational innovations for diverse student groups in varied educational settings. Understanding issues related to large-scale interventions will be particularly important for the U.S., as the science education system embraces new science standards [National Research Council, [2011] A framework for K-12 science education: Practices, crosscutting concepts, and core ideas. Washington, DC: National Research Council.]. In our introduction to the special issue, we discuss critical issues in scaling up educational innovations through which large-scale interventions evolve. First, we describe the process of scaling up an educational innovation. Then, we address challenges in scaling up an innovation. Next, we discuss implications that these challenges present to implementation of an innovation and evaluation of its efficacy and effectiveness. Finally, we briefly introduce the articles that appear in this special issue. ß 2012 Wiley Periodicals, Inc. J Res Sci Teach 49: 271-280, 2012 Keywords: policy; diversity; equity Internationally, current classroom practices have largely been shaped by changing student demographics and accountability policies. In the U.S., the school-aged population is becoming increasingly more diverse, while achievement gaps across content areas persist and in some areas are increasing. At the same time, more demands are being placed on all students as a result of high-stakes testing and accountability policies. Educational innovations take place against the backdrop of changing student demographics and evolving educational policies.This special issue includes manuscripts that develop conceptual frameworks or report on empirical studies addressing large-scale interventions of educational innovations for diverse student groups in varied educational settings. These manuscripts discuss challenges and failures as well as accomplishments and promises of such efforts. Interventions are defined broadly including, but not limited to, curriculum development, teacher professional