This article describes a three-year study assessing change in critical thinking demonstrated in essays written for regular class assignments. A rubric was designed and scorers trained to assess critical thinking holistically without knowledge of the writing prompt or author's status. The longitudinal improvement in scores earned by freshmen over three years was significantly related (p less than 0.01) to the difference in scores awarded to freshmen and juniors at a single moment in time. This method can be used to provide an "academic snapshot" of a program, using authentic course work to quantify learning in critical thinking over the undergraduate experience.