ABSTRACT When subjects are repeatedly tested in cognitive assessments, systematic score gains occur. Such retest effects become even greater when test preparation is provided between assessments. In the context of personnel selection, retest gains are often increased by commercial test training, which threatens the fairness of psychological testing because not all candidates can afford such offers. In the present study, computer-based training was freely offered to all candidates as part of the personnel selection procedure. We examined the relationship between repeated cognitive ability measurements in high-stakes settings and the amount of computer-based training before each measurement. Analyses of 212 candidates showed that cognitive ability scores and the amount of prior training were only related on the first assessment but not on the second. There were still retest effects, but the magnitude of score gains was negatively correlated with the amount of initial training and was unrelated to training between assessments. Only the change in training amount was positively correlated with retest effects. We conclude that providing all candidates with preparatory training already before the first assessment substantially increases assessment fairness in the personnel selection process.