Individual differences and development - one dimension or two?

In this chapter, the authors examine the question of whether within-age and between-age differences in intellectual ability are really just two manifestations of the same phenomenon, corresponding to a single theoretical dimension, or whether there is reason to distinguish between the two kinds of variation and consider them as two theoretical dimensions. The authors then demonstrate how the fields of individual differences and development took divergent paths. The authors explore some current theories of within and between-age differences and attempt to draw together evidence to answer the question. The authors conclude with suggestions for directions in future research