This research proposal seeks to advance our current knowledge on the identification of language impairments in bilingual children by examining the differences in patterns of language growth and cognitive/processing skills between bilingual children experiencing first language loss and those with language disorders using retrospective and prospective longitudinal approaches. Hispanic children are disproportionally underrepresented in special education programs and are less likely than other children to be identified as having speech and language impairments. This disproportionality might be due to the difficulty experienced by speech-language pathologists in identifying whether variations in language performance constitute a language disorder or a characteristic of typical bilingual learning. The main challenge in identifying language impairments in Spanish-speaking children lies in our limited understanding of their language growth patterns since most of these children experience a drastic shift in primary language exposure and use from Spanish (home language) to English (school language). This shift in language exposure often results in a temporary period of time in which their Spanish skills are no longer developing and their English skills are not fully developed yet, due to limitations in input rather than learning capabilities. This poses a critical problem for the accurate identification of language disorders in this population because both typically developing bilingual children experiencing first language loss (i.e., a decline in their first language skills due to limitations in input) and bilingual children with language disorders show low grammatical skills in both languages. It is imperative to examine the differences between these two groups of children so that early and accurate identification is possible. The PI has a strong background in language development and assessment in bilingual children, but lacks the necessary methodological skill set to conduct prospective and retrospective longitudinal studies, and the background knowledge to fully understand the role of cognitive/processing skills in language acquisition. The proposed training plan has the following learning objectives: 1. Design and execute retrospective studies to differentiate patterns of language growth between children experiencing first language loss and bilingual children with language impairments using existent longitudinal databases (Mentor: Francis); 2. Develop a strong understanding of cognitive/processing mechanisms and their role in language acquisition (Mentor: Hernandez); 3. Design and execute an innovative prospective study to differentiate patterns of language growth and cognitive/processing skills between children experiencing first language loss and bilingual children with language impairments using clinical samples (mentors: Francis and Lesaux); and, 4. Transition to scientific independence (Mentors: Fletcher and Francis). This study will improve the accuracy of language assessment practices for Spanish-speaking children by differentiating patterns of first language loss from language impairments.