The design of educational software interfaces is a complex task, given its high domain dependency and multidisciplinary nature. It requires that teachers' knowledge and pedagogical beliefs be incorporated into the interface, posing a challenge to both teachers and designers, as they have to act as partners from the earliest phases of the process, sharing their knowledge. The present work investigates the strategies designers used when paired with experienced teachers, to design two interfaces on chemistry, evaluating how designers work with subjects they know little about, in the initial phases of the design process. Our observations demonstrate that although experienced and non-experienced designers use different strategies to couple with the design task, both approached the task in a depth-first manner. These results should not be generalized, because few subjects were investigated, but point to the importance of being familiar with the knowledge domain--which poses a challenge for designers. (Contains 10 figures.)