Compared with controls , children who had ADHD had higher odds of externalizing ( odds ratio [ OR ] , 11.0 ; 95 % confidence interval [ CI ] , 5.6-21 .6 ; P < .001 ) and internalizing ( OR , 2.9 ; 95 % CI , 1.2-7 .2 ; P = .02 ) disorders ; poorer reading ( effect size , -0.66 ) and mathematics ( effect size , -0.69 ) performance ; and more peer problems ( P < .001 ) .