Achievement typically refers to knowledge and skills that are formally taught in academic settings. However, this definition of achievement can be broadened to include any ability that is valued and taught in a particular cultural setting (e.g., hunting, dancing, or computer programming). Aptitude refers to an individual’s characteristics that indicate the potential to develop a culturally valued ability, given the right circumstances. The difference between aptitudes and achievement at the definitional level is reasonably clear. However, at the measurement level, the distinction becomes rather murky.
Potential, which is latent within a person, is impossible to observe directly. It must be inferred by measuring characteristics that either are typically associated with an ability or are predictive of the future development of the ability. Most of the time, aptitude is assessed by measuring abilities that are considered to be necessary precursors of achievement. For example, children who understand speech have greater aptitude for reading comprehension than do children who do not understand speech. Such precursors may themselves be a form of achievement. For example, it is possible for researchers to consider students’ knowledge of history as an outcome variable that is intrinsically valuable. However, some researchers may measure knowledge of history as a predictor of being able to construct a well-reasoned essay on politics. Thus, aptitude and achievement tests are not distinguished by their content but by how they are used. If we use a test to measure current mastery of a culturally valued ability, it is an achievement test. If we use a test to explain or forecast mastery of a culturally valued ability, it is an aptitude test.
IQ tests are primarily used as aptitude tests. However, an inspection of the contents of most IQ tests reveals that many test items could be repurposed as items in an achievement test (e.g., vocabulary, general knowledge, and mental arithmetic items). Sometimes the normal roles of reading tests and IQ tests are reversed, such as when neuropsychologists estimate loss of function following a brain injury by comparing current IQ to performance on a word-reading test.
A simple method to distinguish between aptitude and achievement is to ask, “Do I care about whether a child has the ability measured by this test because it is inherently valuable or because it is associated with some other ability (the one that I actually care about)?” Most people want children to be able to comprehend what they read. Thus, reading tests are typically achievement tests. Most people are not particularly concerned about how well children can reorder numbers and letters in their heads. Thus, the WISC-IV Number-Letter Sequencing subtest is typically used as an aptitude test, presumably because the ability it measures is a necessary component of being able to master algebra, program computers, follow the chain of logic presented by debating candidates, and other skills that people in our culture care about.
This post is an excerpt from:
Schneider, W. J. (2013). Principles of assessment of aptitude and achievement. In D. Saklofske, C. Reynolds, & V. Schwean (Eds.), Oxford handbook of psychological assessment of children and adolescents (pp. 286–330). New York: Oxford University Press.