The period fused learner-centered, problem-driven approaches with formal design methods, elevating problems as the organizing principle of instruction. Problem-Based Learning placed real cross-disciplinary problems at the heart of learning, promoting small-group collaboration and facilitator-guided inquiry that linked theory with practice. Instructional Systems Design principles began codifying design heuristics, while research on cognitive engagement and self-explanations highlighted how autonomy and explicit explanations boost problem solving and transfer.