The history of research on learning is studded with clues concerning the reciprocal relation between intelligence and achievement, which is the theme of this chapter. Academic ability is a kind of intelligence most relevant to academic domains, such as the verbal domain and the mathematical domain. The two important components of verbal ability are decoding and reading comprehension, whereas two important components of mathematical ability are arithmetic computation and problem solving. Mathematical ability refers to learning and performing on tasks that involve numbers. In examining the theme of the chapter, it is useful to consider the classic distinction between fluid intelligence (cognitive ability that is independent of specific knowledge) and crystallized intelligence (cognitive ability that depends on specific knowledge). Crystallized intelligence is important for education because it can be changed through appropriate opportunities for learning.