For nearly a half a century, research has found that signed languages (e.g., American Sign Language, ASL) are comparable to spoken languages (e.g., English) when it comes to meeting the criteria of linguistic principles for a human language. However, there is limited research available on the topic of signed language disorders, even though they occur with a similar incidence to disorders in spoken language (Cripps et al., 2016: 110–12). The present study aimed to assess the effectiveness in diagnostic and therapeutic activities of two language professionals, Speech-Language Pathologists and ASL Specialists, working with deaf children who exhibit developmental signed language deficits. Pre- and post-research interviews with professionals and observations of professional–student interactions were conducted. This study occurred at a residential school for the deaf with an immersive ASL environment. Due to the lack of knowledge and resources available to language professionals working with deaf children, results suggest that deaf children are not receiving appropriate language intervention. Furthermore, current professionals identified that there is a specific need for a signed language professional, such as signed language pathologist, to specialise in the diagnosis and treatment of individuals with signed language delay and/or disorders.