Spearman's law of diminishing returns (SLODR) refers to the diminishing influence of g at higher g levels. In this study, we used factor mixture modeling to investigate SLODR in the Differential Ability Scales—2nd Edition (DAS–II). Evidence of SLODR was found. The mean and covariance structure among DAS–II subtests were best described by a 2-class confirmatory factor model with class-specific g means, Gf-specific variance (although evidence was mixed), g variance, and subtest residual variance. Higher levels of g were characterized by less g factor variance, and standardized g loadings decreased at higher ability levels. Interpretative weight of IQ composite and subtest scores may depend on the level of g.