This quasi-experimental, nonequivalent control group study compared the impact of Ennis's (1989) mixed instructional methodology to the immersion methodology on the development of critical thinking in a multicultural, undergraduate senior-year learning community. A convenience sample of students (n =171) were selected from four sections of a course offered at a public research university. The quantitative data consisted of participants' responses to the Watson Glaser Critical Thinking Appraisal (WGCTA) Forms A and B and the qualitative data was collected from an in-class assignment. A MANCOVA found no significant differences between the intervention and control groups' overall and five WGCTA subscale scores. A Multiple Regression found no relationship between many of the predictor variables (age, gender, race/ethnicity, overall GPA, science GPA, math GPA, semester credit load, and whether the student was a Pell grant recipient) and WGCTA posttest total score. However, two variables made unique contributions to explaining the criterion variable and both were associated with decreased WGCTA posttest total scores. Combined, these variables explained 19% of the variance in WGCTA posttest scores. The results suggested that senior-year undergraduates need tailored interventions to foster critical thinking skills development. Provisional, open, and axial coding methodology analyzed the qualitative data. Three themes revealing a spectrum of thinking and reasoning skills emerged. A noteworthy finding from the qualitative analysis was the volume of data coded at the theme "Reflections and Concerns." Rather than providing evidence of critical thinking skills, the data expressed students' concerns for the future, reflections on personal growth, or reflections on the tenure as a college student. This theme cut across intervention or control group membership, all levels of WGCTA performance sub-groups, and all levels of individual academic performance. This study inadvertently opened a window into the unique emotional and thinking states of late tenure undergraduate students, perhaps offering insight to why students are less disposed to using critical thinking skills at the end of their college tenure. [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.]