This study contrasted the effects of two task messages, evaluative or non-evaluative, on mathematics performance, affect, and intrinsic task motivation. One hundred-twenty secondary-school students aged 17-21 years were delivered one of the two messages, or assigned to a control condition, before completing a mathematics task, measures of message appraisals (challenge and threat), affect (pleasantness, arousal, dominance), and a behavioural indication of intrinsic task motivation. The evaluative message raised performance only in males, while for females both messages decreased intrinsic motivation for the task, probably due to stereotype threat. Implications for future research and educational practices are discussed.