To be effective, writers must understand what knowledge they share with the audience and what they do not. Achieving this understanding is made difficult by the knowledge effect—a tendency of individuals to assume that their own knowledge is shared by others. Understanding the knowledge effect and methods for reducing it is potentially useful for understanding and teaching writing. In Study 1, we explored the impact of an individual's knowledge of technical terms on that person's ability to estimate other people's understanding of those terms. We assessed how individuals' familiarity with technical terms influenced their predictions that college freshmen and college graduates would understand those terms. Results indicate that familiarity with the meaning of technical terms leads to substantial overestimation of others' knowledge. In Study 2, we evaluated an online tutor designed to improve writers' predictions of other's word knowledge by providing them with feedback on the accuracy of their judgments.