Teaching physical computing has become more prevalent in the past several decades as the maker movement has popularized microcontroller kits as a way to engage students in learning about and creating with technology. Depending on the design of the kit, students can be exposed to concepts in electronics, computer science and design of computational objects. We argue that the concepts students are exposed to depend on the modularity of the hardware and software tools. We define the level of modularity based on two interdependent characteristics: transparency and affordances for interaction. The transparency affects what is hidden or visible to the learner, while the affordances for interaction regulate how users manipulate and combine elements when constructing a computational artifact. Within this study, we examine the transparency and affordances for interaction of the physical computing hardware tools. Using our findings from this examination, we layout a framework that outlines spectrum of modularity that can be provided to facilitate learning with maker kits.