Both systematic and heuristic methods are common practice when designing. Yet, in teaching students how to design, heuristic methods are typically only granted a secondary role. So, how do designers and students develop a mindset for using heuristic methods? In this paper, we study how prior knowledge (about heuristic methods and their usage) and preference (for using heuristic methods) relate to the reported use of heuristic methods when designing. Drawing on a survey among 304 students enrolled in a master-level course on design theory and methodology, we investigated method usage for five activities in the basic design cycle: (1) analysis, (2) synthesis, (3) simulation, (4) evaluation and (5) decision-making. The results of the study showed that knowledge and preference both influence method usage. Additionally, the results showed that for all activities except evaluation, knowledge indirectly influenced method usage through a ‘complementary’ mediation of method preference.