Purpose: This study aimed to develop and validate a screening questionnaire for the early identification of language difficulties in Brazilian Portuguese-speaking preschool children. Method: The article is divided into two studies. In the first study, we reported the theoretical principles that guided the development of the Screening for Identification of Oral Language Difficulties by Preschool Teachers (SIOLD) and tested the validity of its structure. The psychometric properties of the SIOLD were tested using a sample of 754 children attending Year 1 of preschool. Thirty-two teachers coming from eight different schools completed individual questionnaires for all their students. Confirmatory factor analysis was used to assess the validity of the SIOLD. In the second study, we investigated the accuracy of the questionnaire for identifying children with oral language difficulties using a different sample of 100 preschool children. Using receiver operating characteristic and precision recall curves, we assessed the sensitivity and specificity of the SIOLD to identify children who showed impaired language performance in a short battery of tests. Results: The SIOLD has been shown to be a valid and accurate questionnaire for assessing the form and content of oral language in preschool children. It showed good accuracy, with sensitivity ranging between 0.750 and 0.857 and specificity of 0.946 for the identification of language difficulties. Among the cases positively identified by the SIOLD as having language difficulties, 54.5% were true cases of language disorders, while 45.5% were false alarms. The combination of these findings shows that the SIOLD overpredicts positive cases but identifies most children with true language disorders and passes most children without language disorders, as required of a good screening test. Conclusions: The questionnaire provides a useful tool for enabling Brazilian teachers to refer children with language difficulties to the speech-language services. The theoretical and clinical implications are discussed.