Broad instructional methods like "interactive engagement" have been shown to be effective, but such general characterization provides little guidance on the details of how to structure instructional materials. In this study, we seek instructional specificity by comparing two ways of using an analogy to learn a target physical principle: (i) applying the analogy to the target physical domain on a "case-by-case" basis and (ii) using the analogy to create a "general rule" in the target physical domain. In the discussion sections of a large, introductory physics course (N = 231), students who sought a "general rule" were better able to discover and apply a correct physics principle than students who analyzed the examples "case by case." The difference persisted at a reduced level after subsequent direct instruction. We argue that students who performed case-by-case analyses were more likely to focus on idiosyncratic problem-specific features rather than the deep structural features. This study provides an example of investigations into how the specific structure of instructional materials can be consequential for what is learned.