Why is it important to differentiate multilingual children and children with Developmental Language Disorder (DLD)?

Language abilities develop very quickly during childhood, showing particular variability at a preschool age, where children’s language is subject to the effect of both genetic and environmental factors. Much research has tried to identify the core sources of language variability in early language learning and the best possible environment for supporting this process. Some arguments proposed to account for this variability are based on impaired cognitive abilities such as working memory or attention skills: this is the case, for example, for children with Developmental Language Disorder, DLD, or Attention Deficit Hyperactivity Disorder, ADHD. Other studies attribute the source of poor language ability in some preschool children to insufficient input from a particular language, such as in cases of children growing up in an environment with different linguistic characteristics, including multilingual children or those who speak a minority language.

Despite the different approaches adopted in research, it is reported in many studies that the linguistic abilities of many children who are learning a second language appear similar to those of monolingual children of the same age with a DLD. These similarities can cause misidentification of underlying causes, with a risk of both under- and over-diagnoses of a language disorder in multilingual children, and an overall lack of confidence on the part of both carers and teachers regarding how to deal with learning multiple languages at preschool stage. This problem is compounded by the fact that the tasks typically used in the diagnostic procedure are generally standardised based on monolingual speakers, which can result in a severe disadvantage for multilingual children, especially for those who have not reached a mature level of competence in the language of testing.