Halford, Wilson & Phillips argue that cognitive development is driven by in
creases in processing capacity. We suggest that changes in relational knowl
edge are as important or more so. We present evidence that 3-year-olds' ana
logical abilities are sharply improved by teaching them relational labels;
over a 30-minute experimental session children gained approximately 2 years
in effective performance. These results mandate caution interpreting age-r
elated change as indicating maturational change, and call for a deeper cons
ideration of the role of epistemological change in cognitive development.