While the move to anchored scales has been an improvement in the standardization of field performance evaluation, these tools have not been found to consistently discriminate among student performances or identify students experiencing clinical difficulties. This article presents two efforts to redress this problem. The use of a new practice-based scale incorporating field instructors' language and conceptual dimensions of practice did not improve the discrimination of student performance. An alternative evaluation system that involved matching students to a standardized set of more holistic, realistic vignettes did improve field instructors' discrimination of student performances and facilitated the identification of students experiencing clinical difficulties. Implications for field evaluation methodologies are discussed. (Contains 2 figures.)