The study of decision-making by public officials in administrative settings has been a mainstay of law and society scholarship for decades. The methodological challenges posed by this research agenda are well understood: how can socio-legal researchers get inside the heads of legal decision-makers in order to understand the uses of official discretion? This article describes an ethnographic technique the authors developed to help them penetrate the decision-making practices of criminal justice social workers in writing pre-sentence reports for the courts. This technique, called shadow writing, involved a particular form of participant observation whereby the researcher mimicked the process of report writing in parallel with the social workers. By comparing these shadow reports with the real reports in a training-like setting, the social workers revealed in detail the subtleties of their communicative strategies embedded in particular reports and their sensibilities about report writing more generally