The validity of g is most conspicuous in scholastic performance, not because g-loaded tests measure specifically what is taught in school, but because g is intrinsic to learning novel material, grasping concepts, distinctions, and meanings... The most critical tool for scholastic learning beyond the primary grades— reading comprehension—is probably the most highly g-loaded attainment in the course of elementary education.

p. 270; As cited in: Melissa A. Bray, Thomas J. Kehle (2011) The Oxford Handbook of School Psychology. p. 65 - The g factor: The science of mental ability (1998)