Three related studies replicated and extended previous work (J.A. Danielson et al. (2003), "Educational Technology Research and Development," 51(3), 63-81) involving the Diagnostic Pathfinder (dP) (previously Problem List Generator [PLG]), a cognitive tool for learning diagnostic problem solving. In studies 1 and 2, groups of 126 and 113 veterinary students, respectively, used the dP to complete case-based homework; groups of 120 and 199, respectively, used an alternative method. Students in the dP groups scored significantly higher (p = 0.000 and 0.003, respectively) on final exams than those in control groups. In the third study, 552 veterinary students responding to a questionnaire indicated that the dP's gating and data synthesis activities aided learning. The dP's feedback and requirement of completeness appear to aid learning most.