Bruer is president of the James S. McDonnell Foundation in St. Louis and the author of The Myth of the First Three Years: A New Understanding of Early Brain Development and Lifelong Learning. He argues that advocates of the "critical periods" theory of brain development have misinterpreted the research, resulting in a potentially disproportionate channeling of resources toward early childhood education. Bruer tells FRONTLINE, "Investing all or most of our [resources] in early education as opposed to remedial work in the early grades, or even junior high school and high school, may not be the best return on our investment."

Nelson is the director of the Center for Neurobehavioral Development at the University of Minnesota, where he is a professor at the Institute of Child Development. In this interview, he describes the recent research that suggests changes in the prefrontal cortex during adolescence may influence teens' ability to regulate their emotions. He tells FRONTLINE, "I think that neuroscientists have felt for many years that the brain is remarkably pliable and remains pliable for a fair number of years. The concept that the first three years of life is when there's the most malleability and, after that, we lose it, is based on a misreading of some of the most basic neuroscience work."

Shonkoff is dean of the Heller School of Social Policy and Management and professor of human development and social policy at Brandeis University. He recently served as chair of the Committee on Integrating the Science of Early Childhood Development, under the auspices of the Board on Children, Youth, and Families of the National Academy of Sciences and the Institute of Medicine, and co-edited its final report, From Neurons to Neighborhoods: The Science of Early Childhood Development. He believes that public policy can, and should, be informed by science, but that it's important to "be careful about what's not quite ready for prime time yet, in terms of application."

In the popular press, much has been made of research indicating that there are certain crucial periods during which children must be exposed to specific stimuli or risk missing important developmental steps. FRONTLINE producer Sarah Spinks examines the science behind these claims and finds that, for the most part, human learning and development is not limited to certain critical periods, but takes place throughout a person's lifespan.

As researchers discover more and more about the teenage brain, it is natural that parents, educators, and policymakers want to apply this new knowledge as quickly as possible in homes and classrooms. However, as an examination of the controversy over what has become known as the zero-to-three movement shows, there are potential pitfalls when advocacy groups and others attempt prematurely to apply science to public policy.