We examined how different kinds of rating formats, and their interaction with purposes of rating (administrative vs. developmental), induced different performance rating processes and their consequences for rating accuracy. In two experiments, participants rated seven targets presented via videotapes using modes of rating giving access to (a) descriptive knowledge (rating scales were a target's observable behaviors: Descriptive Behavior-DB), (b) evaluative knowledge (rating scales were others' behaviors that the target tended to afford: Evaluative Behavior-EB), or (c) a mix of the two knowledge types (rating scales were traits). Indexes of discriminability (within- and between-ratee discriminability) and of accuracy (differential elevation and differential accuracy) were collected. The results showed that EB rating scales led to higher between-ratee discriminability and differential elevation than other modes of rating, whereas DB rating scales led to higher within-ratee discriminability than the other modes. Our results indicate that EB rating scales are more suited to comparing different ratees (e.g., an administrative purpose for rating), whereas DB scales are more suited to identifying strengths and weaknesses of a particular ratee (e.g., a developmental purpose). Our experiments are the first to apply dual-knowledge (descriptive vs. evaluative) theory to a performance appraisal context and to examine rating purpose in interaction with these two forms of person knowledge. The results, consistent with theoretical predictions, indicate that using rating scales with different types of content as a function of the rating purpose will produce more appropriate performance ratings.