if there are factors that would tend to make early high scores overestimates, I would say that they would almost certainly be found in the "crystallized knowledge" areas of the tests, such as vocabulary, where early environmental enrichment or deprivation could make a huge difference in test performance, giving very young children with relatively enriched environments an apparent "edge" that might not be maintained once children from relatively deprived environments entered school and, hopefully, had more exposure to opportunities to acquire the same level of knowledge.