Case-based instruction (CBI) provides a way to vicariously engage preservice teachers in their future teaching realities. However, little research has considered how different discussion facilitation strategies relate to the development of preservice teachers' instructional design (ID) skills. We used an embedded mixed methods case study research design to compare differences in how preservice teachers approached the ID process when engaged in one of two strategies: discussions guided by pre-constructed prompts and a facilitator and discussions guided by pre-constructed prompts only. Findings revealed that preservice teachers who participated in discussions guided by a facilitator analyzed case problems more deeply, as they identified more sources of inspiration to guide their design choices; considered learner, environmental, and content characteristics more often; and reported spending more time understanding case problems. While most preservice teachers believed they could apply what they learned from participating in CBI to their future profession, preservice teachers receiving prompts only were more positive about the discussion aspect of CBI.