Research has widely demonstrated male superiority in the Mental Rotation Test (MRT). Various explanations have been put forward to account for these differences. We considered gender beliefs and argued that women may fare less well than men partly because they are considered unable to perform this kind of task. Beliefs about spatial ability were experimentally manipulated in samples of 107 female and of 90 male high-school students, divided into three groups, following the instructions: men are better, women are better, general (with no gender reference). Our data show that women who expect to be more able than men and men who expect to be more able than women outperformed their counterparts. MRT performance fell for those expecting to be less able. The effects of induced beliefs on cognitive performance are stressed, particularly in the educational context.