Human cognitive abilities exhibit positive interrelationships that can be represented by a latent general intelligence factor (g). Differentiation hypotheses propose that there are systematic interindividual differences in the strength of g, specifically along the dimensions of ability level (ability differentiation) and age (age differentiation). Despite the potential implications for cognitive theory and assessment, the available evidence on the matter is inconclusive. We present comprehensive analyses of differentiation effects across the lifespan, drawing on the meta-analytic integration of nonlinear factor analyses with German standardization samples (