Research examining students' historical reasoning has heavily relied on evidence in the form of students' written work to make claims about students' ability to reason historically and have argued that the document-based history essay holds the most promise for assessing students' historical thinking (Nokes & De La Paz, 2018). However, relatively little research has sought to understand the extent to which students' written essays are an accurate approximation of students' historical reasoning. The present study is an investigation of the historical reasoning that students engage in during the composing process relative to what is inferable from the essay. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]