With a growing call for an increased emphasis on computing in school curricula, there is a need to make computing accessible to a diversity of learners. One potential approach is to extend the use of physical toolkits, which have been found to encourage collaboration, sustained engagement and effective learning in classrooms in general. However, little is known as to whether and how these benefits can be leveraged in special needs schools, where learners have a spectrum of distinct cognitive and social needs. Here, we investigate how introducing a physical toolkit can support learning about computing concepts for special education needs (SEN) students in their classroom. By tracing how the students' interactions-both with the physical toolkit and with each other-unfolded over time, we demonstrate how the design of both the form factor and the learning tasks embedded in a physical toolkit contribute to collaboration, comprehension and engagement when learning in mixed SEN classrooms.