An ethnographic study investigated conversations during planning meetings and placement rating sessions for selecting and rating freshman composition placement exams. Planning meetings involved the administrative coordinator and two assistants selecting model essays, discussing the rubric, and confirming the final plans for the rating session. Fifteen instructors of first-year composition at a large, public, urban midwestern university holistically rated about 2,000 placement essays over a 4-day period. Conversations were tape recorded, transcribed, and analyzed. Results indicated that, while choosing the model essays, the planning team focused on an informal rubric; during the rating session itself, however, no mention of the informal rubric was made. Most discussions took place around problematic or puzzling essays; ones that fit clearly into a category did not require much discussion. Findings suggest that administrators of holistic assessment sessions should expect discussions during rating sessions to stray far from the terms of the written rubric as the raters struggle to work out the meaning of scores they assign. (A figure listing terms from the "mental rubric" and a figure presenting the written rubric are included.) (RS)