According to an eleven-year-long study by a group of Canadian researchers, it appears that the youngest students in a class are more likely to be diagnosed with attention deficit hyperactivity disorder (ADHD) than peers born at other points in the year. The study , conducted by University of British Columbia researchers and headed up health research analyst Richard Morrow, finds that children born the month of the school’s cut-off date were more likely to receive an ADHD diagnosis than those born just a month later. After studying nearly 930,000 children in British Columbia, which has a cut-off date for enrollment of December 31, it was found that boys born in December were 30 percent more likely to be given an ADHD diagnosis than those born in January. Girls with December birthdays were 70 percent more likely to receive this diagnosis than those born in January. Furthermore, boys and girls with December birthdays were 41 percent and 77 percent more likely, respectively, to be treated with prescription medication for ADHD than those born the following month. While researchers believe their analyses show a relative-age effect in the diagnosis and treatment of children age 6-12 years, they warn that these findings raise concerns about the potential for overdiagnosis and overprescribing in the youngest students because the lack of maturity in younger students may be misinterpreted as symptoms of ADHD. ADHD is currently the most commonly diagnosed neurobehavioral disorder in children. For more information on this study , visit the Canadian Medical Association Journal .