Critical thinking is one of the most desired skills in the workplace, as it assists an individual in solving complex problems and making informed decisions, resulting in their workplace success. Argumentation is one instructional approach that provides students an opportunity to engage in higher-order thinking and improve their communication skills. Argumentative writing provides opportunities to engage in multiple perspectives of a problem, provide evidence for the claim, evaluate evidence, engage in reasoning, and acknowledge self-bias, which automatically engages students in critical thinking. Previous literature has shown that despite the use of interventions and scaffolding approaches, students' argumentative texts lack elements of an argument. The purpose of this qualitative descriptive study was to explore undergraduate engineering students' argument schema with the aim of uncovering gaps in students' knowledge of the different elements of an argument. Data for the study were collected using semi-structured interviews with undergraduate engineering students (n=13) enrolled in the second through senior year of their engineering program at multiple US universities. The interview data was transcribed and analyzed using qualitative content analysis. The results of the study showed variation in students' knowledge of each element of the argument schema. Two types of argument schemas were identified. For each, the elements for which students' knowledge was limited were described and instructional support needed were identified. Recommendations for how instructors can improve students' argumentation skills were provided. [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.]