The authors implemented a cognitive apprenticeship learning community (Collins, Brown, & Newman, 1989) in a class of preservice teachers at the University of Missouri - Columbia to enhance their argumentation and critical thinking skills about complex, educational problems. A detailed rubric based on the literature in argumentation and scientific reasoning was developed to evaluate the students' performance before and after the intervention. The rubric was designed to measure students' (a) conceptions and use of evidence, (b) notions about research and its applicability in evaluating complex social problems, and (c) ability to consider alternative perspectives. This article describes the intervention, the theoretical underpinnings of the rubric, and the use of the rubric in measuring the development of critical thinking in a group of preservice teachers. Strengths and weaknesses of the rubric are outlined and avenues for future research are discussed.