This review of research generates principles for the design of instructional programs that foster critical-thinking dispositions. The dispositional aspect of critical thinking may be considered part of attitudinal memory, readily activated if sufficiently strong. We describe evidence suggesting that ill-structured problem-solving can provide middle schoolers with motivating activities that strengthen critical-thinking dispositions, thus fostering sensitivity to occasions for thinking critically and the inclination for engaging in such practices. The Jasper Series and Decision Making are reviewed as cases of programs for middle level mathematics learning that afford opportunities for ill-structured problem-solving activities that incorporate five important attitude-strengthening elements. Fazio (1995) identified these elements as direct experience, sensory experience, emotional reaction, freely chosen behavior, and attitude rehearsal. We describe how the design of the two mathematics programs incorporates attitude-strengthening elements that can potentially foster critical-thinking dispositions. Based on this review, we present a set of design principles to promote those dispositions. (Contains 2 figures.)