Although a large body of research emphasises the collaborative nature of adolescents' multimodal composing processes in and out of school, little is known about how or why collaborative partnerships might differ across composers or digital tools. Integrating sociocultural and social semiotics theoretical frameworks, this study examined how three pairs of culturally and linguistically diverse Grade 12 students collaboratively composed across three multimodal projects--a website, hypertext literary analysis and podcast--when responding to and analysing literature. Data sources included screen capture and video observations, student design interviews and written reflections. Qualitative data analysis revealed three different types of collaborative partnerships: (1) designer and assistant collaboration, (2) balanced division collaboration and (3) alternating lead collaboration. The division of labor between students was based on the convergence of mediating factors, with students negotiating multiple modes and tools, along with their partner's and their own technical skills, content knowledge and design preferences. These findings demonstrate how collaborative multimodal composing processes were multilayered and offered students flexibility for tailoring unique collaborative partnerships. Implications are discussed for understanding and supporting adolescents' collaborative multimodal composing processes in the classroom.