Purpose: Interprofessional practice requires regular communication between professionals from different disciplines using shared terminology. Within schools, many professionals are tasked with supporting children with language disorders, namely, developmental language disorder (DLD) and/or dyslexia. Limited information exists as to (a) how school-based professionals' definitions of DLD and dyslexia align with research definitions, (b) how different school-based professionals define language disorders, (c) how school-based professionals' definitions of DLD and dyslexia align across professional groups, and (d) how one's definition of a language disorder correlates with other measures of knowledge. Method: In this mixed-methods study, we analyzed 304 definitions of language disorders from school-based professionals using a summative content analysis process. We explored the relationship between definitions and knowledge of disorder characteristics and best practices. Results: Data reflected limited alignment between professional and research definitions of DLD and dyslexia. Common misconceptions related to each disorder were prevalent among school-based professionals' definitions. There were differences between the extent to which professional groups' definitions aligned with research definitions of DLD and dyslexia. Conclusion: Results highlight the need for shared terminology between professional groups and researchers to improve collaborative practices and to narrow the research-to-practice gap.