1. Barell, J. (2007). Problem-based learning: An inquiry approach (2nd ed.). Thousand Oaks, CA: J. Corwin Press.
2. Barrows, H. S. (1988). The tutorial process. Springfield, MA: Southern Illinois University School of Medicine.
3. Baum, S., Viens, J., & Slatin, B. (2005). Multiple intelligences in the elementary classroom: A teacher’s toolkit. New York, NY: Teachers College Press.
4. Belland, B. R., French, B. F., & Ertmer, P. A. (2009). Validity and problem-based learning research: a review of instruments used to assess intended learning outcomes. The Interdisciplinary Journal of Problem-based Learning, 3(1), 59–89.
5. Boud, D., & Feletti, G. (1997). The challenge of problem-based learning (2nd ed.). London: Kogan-Page.