This article takes its outset in findings from an ongoing research project investigating the use of digital and multimodal resources in teacher education (TE) in Norway. The material studied is mandatory assignments in different courses in TE, asking how teacher students collaborate through digital media in their production of texts for learning, and how the design of these literacy practices can be influenced through the teachers' design of the assignments. In focus group interviews the researchers found that the students preferred organizing collaborative processes through Facebook groups rather than through the university's learning management system. This created a space between formal and informal learning, often mediated by ''power users'' performing a curatorial function on behalf of the group. Furthermore, the quality of the processes seemed to depend on how the assignments were designed for different modes and for individual or group work. The tasks that inspired genuine collaborative learning were characterized by a certain complexity in terms of multimodality and technology, or professional knowledge combining academic and practical experience. In other cases tasks to be performed in groups were split between the students, and probably did not add the same value to individual learning. This is discussed as an encounter between the teachers' design of the assignments and the students' design of their learning processes. When teacher students tell us how they work with assignments, they at the same time explain how their knowledge is designed through social and textual practices. Reflections on these practices are relevant to developing their awareness of didactic design in their future profession as teachers.