Classic micro-economic and psychology theories propose different implications of monetary incentives on performance. Empirical studies in sports settings show that athletes generally perform worse when the stakes are higher, while a range of lab studies involving cognitively demanding tasks have led to diverging results, supporting positive, negative and null-effects of higher (vs. lower) stakes. In order to further investigate this issue, we present a pre-registered, randomized, controlled trial of 149 participants solving both anagrams and math addition tasks. We do not find a statistically significant effect of the size of the reward on neither performance, self-reported effort nor intrinsic motivation. We propose that future studies should contrast the potential impact of rewards on different kinds of task, e.g. compare tasks that solely require cognitive effort vs. tasks that require motor skills, as in sports.