As an institution of higher education and as a Hispanic-serving institution, New Mexico State University has a responsibility to its students to provide the skills and experiences necessary for each and every student to become a responsible, reflective citizen, capable of making informed decisions. Postsecondary science has traditionally been taught through lectures. Traditional lecture classes simply do not meet the needs of diverse groups of students in the modern multicultural student body like New Mexico State University's. However, the implementation of nontraditional pedagogy without evaluation of the results is useless as a step to reform; it is necessary to evaluate the results of in situ nontraditional pedagogy to determine its worth. The purpose of this research is to analyze the development and change in students' critical thinking skills, and critical thinking dispositions in single semester in an introductory Environmental Science course. This study utilized a mixed methods approach. The California Critical Thinking Skills Test and the California Critical Thinking Disposition Inventory were administered in the beginning and at the end of the semester. The pretest was used to provide a baseline for each participant against which the posttest score was compared. In addition, student interviews, field notes, and a survey provided qualitative data, which generated themes regarding the development of student critical thinking in this course. The results indicated there were no significant differences in the critical thinking test scores. However, qualitative analysis indicated that students experienced significant changes in critical thinking. Three themes emerged from the qualitative analysis pertaining to the amount of influence on student learning. These themes are active thinking and learning, dialogue, and professor's influence. Due to the conflict between the quantitative and the qualitative results, it is suggested that the critical thinking tests are not sensitive enough to identify minute but important changes in student critical thinking. [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/en-US/products/dissertations/individuals.shtml.]