Researchers from Harvard, University of Southern California, University of Maryland and others have identified though brain research that some stress is toxic makes students vulnerable to learning while other kinds of stress do not. Be sure to watch the videos showing brain architecture in young developing brains as well as overall health development. Some adverse experiences are never 'gotten over' even after 50 years.
Research Traces Impacts of Childhood Adversity. Sarah D. Sparks. 5.16.13. Education Week - Premium Article.