This case study examines the reasoning of a clinical supervisor as she assesses preservice teacher candidates with a state-mandated performance assessment instrument. The supervisor’s evaluations were recorded using video annotation software . The clinical supervisor was asked to annotate the teaching videotapes of three preservice teachers. Findings indicate that the clinical supervisor found it difficult to interpret rubric criteria, often made tenuous claims about candidates’ performance, and tended to require students to design lessons that were artificial demonstrations of mandated competencies.