The aim of this study is to determine the prevalence rate of ODD in school age children, and analyze the variability of the prevalence rates per informant, according to the sources of information, sex, age, and level of agreement between teachers and parents. This is an epidemiological study conducted using a community sample extracted by means of multi-stage stratified sampling. The sample consisted of 1,295 children of both sexes from 6 to 8 years old. For diagnostic evaluation, the Oppositional Defiant Disorder Rating Scale (ODDRS-IV) was used. The estimated global prevalence of ODD, detected by all sources is 16.1%. But if we consider the percentage of subjects detected by only one informant, the prevalence rate is 9.5%. The prevalence according to teachers is 5.1% (95% CI = 3.88–6.31), according to fathers is 9% (95% CI = 7.38–10.54), and according to mothers is 9.7% (95% CI = 8.02–11.29). Teachers report more boys with ODD than girls. Results support the idea of high variability in ODD prevalence rates. Our findings suggest that parents are more prone to detect the disorder than teachers, and that boys present ODD more frequently than girls, only when they are evaluated by their teachers.