This book explores the relationship between language difference and disorder, with particular consideration of multidialectal L1 speakers learning English as an L2. It provides the reader with ready-to-use data on child L2 acquisition at the syntax-semantics interface, and offers both empirical and theoretical support for educational and clinical linguists in order to separate language differences from disorders. It provides researchers and students in applied and educational linguistics and speech-language pathology with a comprehensive understanding of L2 development in previously unidentified groups of bilingual-bidialectal children with different performance in the target language. Developmental linguists, applied linguists and speech-language pathologists will find accessible information on the role of L1 bidialectism in L2 acquisition, as well as valuable implications to language teaching and learning practices and speech-language pathology services in multilingual and multicultural contexts. This volume will be key reading for researchers interested in typical and atypical multilingual development and assessment in educational and clinical linguistics, cognitive sciences, and psychology. It will also appeal to both undergraduate and postgraduate students interested in conducting mixed-method research in language education, linguistics and health sciences.