In recent years many countries have introduced authentic performance-based assessments in their national exam systems. Teachers’ ratings of their own candidates’ performances may suffer from errors of leniency and range restriction. The goal of this study was to examine the impact of manipulating the descriptiveness, balancedness, and polarity of the rating scales on the elevation and spread of the performance ratings. Multivariate multilevel analyses found the psychometric quality of the teachers’ performance ratings to be more favorable for positively unbalanced scales than for balanced scales. Positively unbalanced rating scales yielded the lowest (i.e., least generous) and most discriminative ratings. Based on these findings it was decided to introduce positively unbalanced scales in the national exams for pre-vocational education.