Objective: The study explores the psychometric properties of the Brazilian-Portuguese version of the Working Memory Rating Scale (WMRS-Br) in a population of 355 young children from diverse socioeconomic status and schooling backgrounds. Method: Public and private school teachers completed the WMRS-Br and children were assessed on a range of objective cognitive measures of fluid intelligence, working memory, and attention. Results: Reliability and validity of the WMRS-Br were excellent across the public and private school sample. The WMRS-Br manifested substantial links with objective measures of working memory and medium links with selective attention, switching, and interference suppression. Confirmatory factor analyses suggest that a shorter version of the scale provides an adequate fit to the data. Conclusion: The WMRS-Br represents a valid screening tool in a Latin American context that has the potential to improve the early detection of working memory deficits in children growing up in poverty. (J. of Att. Dis. 2013; XX(X) 1-XX)