1. Littlejohn, A. Understanding Massive Open Online Courses. CEMCA EdTech Notes (2013).
2. Stahl, G. K. T. &, S. D. [Computer-supported collaborative learning: An historical perspective]. Cambridge handbook of the learning sciences [Sawyer, R. K. (ed)] [409–426] (Cambridge University Press, Cambridge, 2006).
3. Vaquero, L. & Cebrian, M. The rich club phenomenon in the classroom. Sci. Rep. 3, 1174 (2013).
4. Ezekiel, E. J. Online education: MOOCs taken by educated few. Nature 503, 342 (2013).
5. Breslow, L. et al. Studying Learning In the Worldwide Classroom: Research into edX's First MOOC. Res. Practice Assess. 8, 13–25 (2013).