Mix, K. S., Huttenlocher, J., & Levine, S. C. (2002). Quantitative development in infancy and early childhood. Oxford, UK: Oxford University Press.
Mix, K. S., Sandhofer, C. M., & Baroody, A. J. (2005). Number words and number concepts: The interplay of verbal and nonverbal quantification in early childhood. In R. V. Kail (Ed.), Advances in Child Development and Behavior (Vol. 33). New York: Academic Press.
Wright, R. J. (1989). Numerical development in the kindergarten year: A teaching experiment. Unpublished doctoral dissertation, University of Georgia.
The descriptions of the levels of the number word sequences, forwards and backwards, and the levels of numeral identification are derived from the work of Professor Bob Wright. His contribution and the contributions of his colleagues to our growing understanding of the role played by counting in developing a rich sense of number are gratefully acknowledged.