Significance Grades and scores on achievement tests are widely used as measures of cognition. This paper examines these measures and their constituent parts. We establish that, on average, grades and achievement tests are generally better predictors of life outcomes than “pure” measures of intelligence. The reason is that they capture aspects of personality that have been shown to be predictive in their own right. All of the standard measures of “intelligence” or “cognition” are influenced by aspects of personality, albeit to varying degrees, depending on the measure. This result has important implications for the interpretation of studies using scores on achievement tests and grades to explain differences in outcomes and for the use of standard cognitive measures to evaluate the effectiveness of public policies.