Confirmatory factor analysis was used to model a multitrait (attention deficit hyperactivity disorder [ADHD]-inattention, ADHD-hyperactivity/impulsivity, oppositional defiant disorder [ODD]) by multisource (mothers, fathers, and teachers) matrix to determine the convergent and discriminant validity of ratings by mothers, fathers, and teachers. Participants were 1,749 elementary school children from the island of Majorca in the Balearic Islands. The results showed good convergent validity for the measures for mothers’ and fathers’ ratings with moderate support for the measures discriminant validity for mothers’ and fathers’ ratings. There was no convergent and discriminant validity, however, between mothers’ and teachers’ as well as fathers’ and teachers’ ratings for the ADHD-IN, ADHD-HI, and ODD measures. The results provide additional evidence that the construct validity of parent and teacher ADHD/ODD rating scales is mostly parent (home) and teacher (school) specific.