Although the estimated prevalence of ADHD in the school population is 5%, various studies carried out in Latin America have obtained higher figures. This descriptive-cross-sectional research analysed the prevalence of ADHD symptomatology in a random and probabilistic sample of 1535 schoolchildren from Cuenca-Ecuador (aged from 72 to 164 months, 51.3% were female and 50% attended public schools). IQ was evaluated using the Raven's Progressive Matrices Test. The ADHD symptomatology was evaluated using the short version of Conners-3. Descriptive statistics, chi-squares and prevalence data were calculated. We found a total prevalence of ADHD symptomatology of 20.3%. A higher prevalence of ADHD symptomatology was reported among girls compared to boys; and in public schools (compared to private schools). These findings may reflect a higher occurrence of ADHD in vulnerable populations that tend to be less well cared for. Although the results do not come from complete individual clinical evaluations, the representativeness of the sample and the simultaneous presence of scores above the cut-off points in the home and school contexts show a worrying situation that should be taken into account by agents responsible for the design of public health and education policies.