1. Behr, M., Harel, G., Post, T. & Lesh, R. (1992). Rational number, ratio and proportion. In D. Grouws (Ed.), Handbook on research of teaching and learning (pp. 296–333). New York, NY: McMillan.
2. Boyer, T. W., Levine, S. C. & Huttenlocher, J. (2008). Development of proportional reasoning: Where young children go wrong. Developmental Psychology, 44(5), 1478–1490.
3. Brousseau, G. (2002). Theory of didactical situations in mathematics. New York, NY: Kluwer Academic Publishers.
4. Common Core State Standards Initiative (2010). Common core state standards for mathematics. Retrieved from
http://www.corestandards.org/Math/
.
5. Cramer, K. & Post, T. (1993). Making connections: A case for proportionality. Arithmetic Teacher, 60(6), 342–346.