The purpose of this article is to (a) provide a detailed description of how one school in the United States developed decision-making guidelines for implementing a speech-language/mental health (SLP/MHP) co-therapy service delivery model, and (b) summarize study findings based on interviews conducted with school-based speech-language pathologists (SLPs), school-based licensed mental health providers (MHPs), and administrators about their perceptions of using this co-therapy model to provide services to students with intellectual/developmental disabilities (e.g., autism) and co-occurring language and mental health support needs. We used qualitative analysis to identify key themes from the 19 interviews we conducted with school-based staff, including SLPs, MHPs and administrators. Thematic analysis indicated that: (a) students demonstrated progress during co-therapy and benefited from its more holistic approach to complex, interdisciplinary content and skills; (b) SLPs felt more confident handling their students' emotional regulation needs, challenging behaviours and/or other mental health support needs; and (c) MHPs felt more confident adapting language to make therapeutic content accessible to their students with language support needs. Interviewees also discussed logistical challenges and recommendations for further guidance/training. Findings from interviews indicate that SLP/MHP co-therapy may offer a promising service delivery option for students with intellectual/developmental disabilities receiving both speech-language and mental health services through their individualized education programs (IEPs).