Learning outcomes have changed drastically over the past decades. To address these new outcomes, including twenty-first-century skills, instructional design (ID) needs a fresh approach. This study examines the impact of learning theories, cognitive processes, and knowledge types on twenty-first-century skills in Indian classrooms. The research introduced a literature-based methodology for assessing variable prevalence and an Educational Practices and Skills Index (EPSI) to gauge the impact of learning theories on these skills. Findings highlight the prevalent use of behaviourist and cognitivist learning theories, especially in sixth and tenth-grade science and mathematics classes. It is observed that twenty-first-century skills, including critical thinking and problem-solving, are only moderately cultivated. A comparison between Indian classroom observations and a vignette study from the literature underscores the efficiency of cognitivist and constructivist approaches in promoting these skills. Consequently, the study recommends the integration of design thinking (DT) as a pedagogical model since it embodies cognitivist and constructivist principles, which should, as our findings indicate, improve twenty-first-century skills.