Self-assessment is an important tool for evaluating behaviour and for gaining self-knowledge. However, self-assessment is prone to biases that contaminate the accuracy of the evaluation. The aim of this study was to evaluate whether the presence of a standard – an objective description of a standard of competent practice – within self-assessment measures would reduce such biases and enhance the validity of self-assessment. Psychology graduate students were randomly assigned to complete self-assessments of research and clinical supervision competency that either included, or did not include, a standard. The presence of a standard had no effect on self-assessment means, but amount of training was associated with perceived competence within the same domain among those who completed the survey with the standard. The findings suggest that the inclusion of a standard has a complex effect on self-assessment scores that does not simply reduce self-enhancement effects but nonetheless improves the construct validity of the measure.