A breaktrough in modeling development is achieved with the overlapping waves model.
On the next page (“Waves”) a fully interactive version of such a model is presented. It can visualize the underlying model using Mathematica 8. Using the so called CDF player you can rotate and modifiy the model in all kinds of ways in your own webbrowser.

Some relevant papers can be send to your email address.

1) The first empircal study using the model is a paper with Sanne van der Ven:
Van der Ven, S. H. G., Boom, J., Kroesbergen, E. H., & Leseman P. P. M. (2012). Microgenetic patterns of children’s multiplication learning: Confirming the Overlapping Waves model by latent growth modeling. Journal of Experimental Child Psychology, 113, 1-19. Epub 2012 Jun 12. DOI:10.1016/j.jecp.2012.02.001
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2 A precursor chapter that explains the idea of an underlying developmental dimension can be downloaded here:
Boom, J. (2009). Measuring moral development: Stages as markers along a Latent Developmental Dimension. In W. Koops, D. Brugman, T.J. Ferguson, & A. Sanders (Eds.). The Development and Structure of Conscience. Hove: Psychology Press.
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3 An older empircal study that puts some of the ideas from paper 2 to test can be downloaded here:
Boom, J., Wouters, J., & Keller, M. (2007). A cross-cultural validation of stage development: A Rasch re-analysis of longitudinal socio-moral reasoning data. Cognitive Development, 22, 213-229.
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4 This new model is decribed in the as yet unpublished manuscript: (sorry… under review)