Likert scales traditionally used in student evaluations of teaching (SET) suffer from several shortcomings, including psychometric deficiencies or ambiguity problems in the interpretation of the results. Assessment instruments with Behavioral Anchored Rating Scales (BARS) offer an alternative to Likert-type questionnaires. This paper describes the construction of an appraisal tool with BARS generated with the participation of 974 students and 15 teachers. The resulting instrument eliminates ambiguity in the interpretation of results and gives objectivity to the evaluation due to the use of unequivocal behavioral examples in the final scale. However, BARS methodology presents the problem of losing behavioral information during scale construction. The BARS methodology presented by the authors introduces an additional step to the traditional procedure, which significantly reduces the loss of information during the scale construction. The authors conclude that the qualitative approach of the proposed instrument facilitates the application of the formative function of the evaluation.