1. Abramovich, S., Higashi, R., Hunkele, T., Schunn, C., & Shoop, R. (2011). An achievement system to increase achievement motivation. Paper presented at the games learning society 7.0, Madison, WI.
2. Abramovich, S., Schunn, C., & Higashi, R. M. (2013). Are badges useful in education? It depends upon the type of badge and expertise of learner. Educational Technology Research and Development, 61(2), 217–232.
3. Ahn, J., Pellicone, A., & Butler, B. S. (2014). Open badges for education: What are the implications at the intersection of open systems and badging? Research in Learning Technology, 22, 1–9. doi: 10.3402/rlt.v22.23563 .
4. Bandura, A. (1993). Perceived self-efficacy in cognitive development and functioning. Educational Psychologist, 28(2), 117–148.
5. Covington, M. V. (2000). Intrinsic versus extrinsic motivation in schools: A reconciliation. Current Directions in Psychological Science, 9, 22–25.