Asthma in children that is poorly controlled more than doubles the cost of treating it and hurts their school performance, U.S. researchers say. Dr. Stanley Szefler, a professor of pediatrics at National Jewish Health who led the study, and colleagues studied 628 children ages 6-12 with severe or difficult-to-treat asthma. The researchers evaluated direct medical costs -- medications, unscheduled office and emergency visits, and hospital admissions -- and indirect costs such as school days lost. Costs were evaluated at baseline, 12 months and 24 months. Patients were divided into three groups -- very poorly controlled, not well-controlled and well-controlled asthma, using National Institute of Health guidelines. Very poorly controlled asthma patients incurred at baseline an average of $7,846 in costs associated with asthma, compared with $3,526 for not well controlled asthma patients and $3,766 for well-controlled asthma. Two years later, costs for very poorly controlled asthma patients increased to $8,880 while costs for those with well-controlled asthma dropped to $1,861. All costs are in 2002 dollars and costs in 2011 dollars would be about 25 percent greater, the researchers say. The study, published in The Archives of Allergy, Asthma & Immunology, finds children with very poorly controlled asthma finds missed an average of 18 days of school each year, compared with two or less for other asthma patients.