There is a growing body of research indicating a connection between time spent in nature and the management or mitigation of ADD and ADHD symptoms. We happened to run across an abstract on Pub Med of a paper that indicates just this. Although this is not the full paper it does, in brief, outline the conclusions of the study in question.
Check it out: http://www.ncbi.nlm.nih.gov/pubmed/18725656
As an outdoor professional I see the effects first hand of time outside in the children I work with. Almost universally the children that come to my programs with attention deficit labels demonstrate an incredible capacity to engage with and learn about the natural world. Being outside seems to calm and focus children who have trouble staying put in the classroom and give them the opportunity to receive the high volume and variety of environmental input that they are predisposed to processing well. For these reasons I perceive these “disorders” as strengths out of context.
If you are interested in reading more about the relationship between our children’s development and contact with the natural world, check out Richard Louv’s book: Last Child in the Woods http://richardlouv.com/books/last-child/