In the present meta-analysis the effects of developmental level on the correlation between simple and complex span tasks were investigated. Simple span-complex span correlation coefficients presented in 52 independent samples (7,060 participants) were regressed on a variable representing mean age of sample (range: 4.96-22.80 years), using analyses adapted for meta-analytic purposes. The results showed strong positive relations between mean age of sample and simple span-complex span correlation coefficients, suggesting that the relation between simple and complex span tasks became stronger with increasing age. These results could not be accounted for by study-related differences in measurement reliability, restricted range, or sample size. A new theoretical account explaining these findings is outlined. (Contains 4 tables, 3 figures and 3 footnotes.)