This article examines whether noncognitive skills—measured both by personality traits and by economic preference parameters—influence cognitive tests’ performance. The basic idea is that noncognitive skills might affect the effort people put into a test to obtain good results. We experimentally varied the rewards for questions in a cognitive test to measure to what extent people are sensitive to financial incentives. To distinguish increased mental effort from extra time investments, we also varied the questions’ time constraints. Subjects with favorable personality traits such as high performance motivation and an internal locus of control perform relatively well in the absence of rewards, consistent with a model in which trying as hard as you can is the best strategy. In contrast, favorable economic preference parameters (low discount rate, low risk aversion) are associated with increases in time investments when incentives are introduced, consistent with a rational economic model in which people only invest when there are monetary returns. The main conclusion is that individual behavior at cognitive tests depends on noncognitive skills. (jel j20, j24).