The 20th century was based on local linear engineering of complicated systems. We made cars, airplanes and chemical plants for example. The 21st century has opened a new basis for holistic non-linear design of complex systems, such as the Internet and air traffic management. Interconnectivity, communication and interaction are major attributes of our evolving society. But, more interestingly, we have started to understand that chaos theory may be more important than reductionism, to better understand and thrive on Earth. Systems need to be investigated and tested as wholes, which requires a cross-disciplinary approach and new conceptual principles and tools. Consequently, schools cannot continue to only teach isolated disciplines based on simple reductionism. Science, Technology, Engineering, and Mathematics (STEM) should also be integrated together with the Arts to promote creativity together with rationalization, and move (back) to STEAM (with an "A" for Arts). This concept shift emphasizes the possibility of longer-term socio-technical futures instead of short-term financial predictions that currently lead to uncontrolled economies. Human-centred design (HCD) can contribute to not only improving education technologies, systems and practices, but also as a discipline offering an integrated approach to learning by doing, expressing and critiquing, exploring possible futures, and understanding complex systems: HCD supports learning thinking.