Where most educational research is about how education was or is, design research is about how education could be (Schwartz et al., 2008). You do design research if you need to solve a complex problem (Plomp & Nieveen, 2013) or if you have an idea how you could improve education, or perhaps achieve new and important learning goals. If there is no existing educational setting in which you can study what you want to study, you can design such setting yourself. What you then do is research-based design, and subsequently design-based research. Together they can be called design research, but there are many other names for this type of research: educational design research, design experiments, or design studies. The design work and research process are then like the two hands of Escher drawing each other.
Plomp, T., & Nieveen, N. (2013). Educational design research: Introduction and illustrative cases. Enschede: SLO.Retrieved from: http://www.international.slo.nl
Schwartz, D. L., Chang, J., & Martin, L. (2008). Instrumentation and innovation in design experiments: Taking the turn towards efficiency. In A. E. Kelly, R. A. Lesh, & J. Y. Baek (Eds.), Handbook of design research methods in education: Innovations in science, technology, engineering, and mathematics learning and teaching (pp. 47-67). London: Routledge.
Image retrieved from here.