This article reports on an investigation into the correlations between students' understandings of introductory astronomy concepts and the correctness and coherency of their written responses to targeted Lecture- Tutorial questions. We assessed the correctness and coherency of responses from 454 college-level, general education, introductory astronomy students enrolled in courses taught in the spring of 2010, 2011, and 2012. We hypothesized that students who consistently provided responses with high levels of correctness and coherency would outperform students who did not on multiple measures of astronomy content knowledge. We compared students' correctness and coherency scores to their normalized gains on the Light and Spectroscopy Concept Inventory (LSCI) and to their scores on closely related exam items. Our analysis revealed that no significant correlations exist between students' correctness and coherency scores and their LSCI gain scores or exam item scores. However, the participant group in our study did achieve high scores on the LSCI and on closely related exam items. We hypothesized that these differences are due to the discussions that take place between students, which suggests that instructors who teach with active engagement instructional strategies should focus their implementation on ensuring that their students fully engage in the richest possible discourse.