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."

Carskadon is a professor of psychiatry and human behavior at Brown University and director of chronobiology and sleep research at E.P. Bradley Hospital in Providence, R.I. Her research focuses on the interrelation between the circadian timing system and sleep/wake patterns of children and adolescents. Her work has highlighted the consequences of insufficient sleep in adolescents, as well as concerns about early school starting times.

Galinsky is the president and co-founder of the Families and Work Institute, a Manhattan-based nonprofit organization conducting research on the changing family, workplace, and community. She is also the author of Ask the Children, a book based on her extensive survey of more than 1,000 children that measured how they felt about their family relationships and their parents' work lives.

Giedd is a neuroscientist at the National Institute of Mental Health. Recently, he spearheaded research showing for the first time that there is a wave of growth and change in the adolescent brain. He believes that what teens do during their adolescent years -- whether it's playing sports or playing video games -- can affect how their brains develop.

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."

Smith is a professor of psychology at Trent University in Peterborough, Ontario. His research focuses on increasing understanding of how the brain, during sleep, continues to process information that was learned while awake. In this interview with FRONTLINE, Smith recounts the human and animal studies that suggest a good night's sleep helps reinforce the cognitive and motor tasks learned during the day.

Yurgelun-Todd is the director of neuropsychology and cognitive neuroimaging at McLean Hospital in Belmont, Mass. Her recent work suggests that teens' brains actually work differently than adults' when processing emotional information from external stimuli.