Researchers of high-stakes, subjectively scored writing assessments have done much work to better understand the process that raters go through in applying a rating scale to a language performance to arrive at a score. However, there is still unexplained, systematic variability in rater scoring that resists rater training (see Hoyt & Kerns, 1999; McNamara, 1996; Weigle, 2002; Weir, 2005). The consideration of individual differences in rater cognition may explain some of this rater variability. This mixed-method exploratory case study (Yin, 2009) examined rater decision making in a high-stakes writing assessment for preservice teachers in Quebec, Canada, focussing on individual differences in decision-making style, or "stylistic differences in cognitive style that could affect decision-making" (Thunholm, 2004, p. 932). The General Decision Making Style Inventory questionnaire (Scott & Bruce, 1995) was administered to six raters of a high-stakes writing exam in Quebec, and information on the following rater behaviours was also collected for their potential for providing additional information on individual decision-making style (DMS): (a) the frequency at which a rater decides to defer his or her score, (b) the underuse of failing score levels, and (c) the comments provided by raters during the exam rating about their decisions (collected through "write-aloud" protocols; Gigerenzer & Hoffrage, 1995). The relative merits of each of these sources of data are discussed in terms of their potential for tapping into the construct of rater DMS. Although score effects of DMS have yet to be established, it is concluded that despite the exploratory nature of this study, there is potential for the consideration of individual sociocognitive differences in accounting for some rater variability in scoring. (Contains 2 figures, 5 tables and 3 footnotes.)