In this mixed method study I evaluated the relationship between teachers' perceptions of text complexity and data of text complexity assessed by standard and non-standard measures in the disciplines of English Language Arts (ELA), science, and social studies. For the quantitative portion of this study, I evaluated and correlated the text complexity of forty-four literary and informational texts from grades 6-12 extracted from a state-recommended reading list by using two standard measures (Lexile Levels and the Flesch-Kincaid Readability Formula) and one non-standard measure (nominal structures). Additionally, I administered a survey to one hundred and eleven teachers from public and non-public schools aimed at gaining demographic data and determining teachers' perceptions of text complexity by asking them to rate the level of complexity of all forty-five texts using a Likert scale. Teacher ratings of text complexity were correlated with the scores calculated from the standard and non-standard measures. For the qualitative portion of this study, a linguistic analysis was conducted, and follow-up interviews were scheduled with participating teachers to further gauge teachers' perceptions and understanding of text complexity. Three case studies were also created using the existing pool of interviewees. This research aimed to add to the connections between text complexity and teachers' perceptions, especially as related to preparing secondary students for college and/or careers. It also aimed to provide information that could be used for ELA, science, and social studies teacher professional development by revealing attitudinal and practical issues faced by teachers when creating and implementing curriculum, as well as focus areas so that students can navigate complex texts with precision. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]