The purpose of this study was to investigate the intra-rater and inter-rater reliability of the Critical Thinking Analytic Rubric (CTAR). The CTAR is composed of 6 rubric categories: interpretation, analysis, evaluation, inference, explanation, and disposition. To investigate inter-rater reliability, two trained raters scored four sets of performance-based student work samples derived from a pilot study and subsequent larger study. The two raters also blindly scored a subset of student work samples a second time to investigate intra-rater reliability. Participants in this study were high school seniors enrolled in a college preparation course. Both raters showed acceptable levels of intra-rater reliability ([alpha] greater than or equal to 0.70) in five of the six rubric categories. One rater showed poor consistency ([alpha] = 0.56) for the analysis category of the rubric, while the other rater showed excellent consistency ([alpha] = 0.91) for the same category suggesting the need for further training of the former rater. The results of the inter-rater reliability investigation demonstrate acceptable levels of consistency ([alpha] greater than or equal to 0.70) in all rubric categories. This investigation demonstrated that the CTAR can be used by raters to score student work samples in a consistent manner. (Contains 5 tables and 4 figures.)