The purpose of this quantitative, causal-comparative study was to determine how, and to what degree learning methods (student-centered or instructor-centered) and gender independently or interactively made a difference in adult student achievement. The Wechsler Individual Achievement Test Third Edition (WIAT-III) was utilized to measure achievement. Data were collected by using convenience sampling from the target population of adult college students, with a final sample of 139 participants. Cognitive learning theory, constructivist learning theory, and adult learning theory were used to guide this study. The research questions were: To what extent, if any, is there a difference in adult student achievement, as measured by the WIAT-III between students who learn with the student-centered method and students who learn with the instructor-centered method, to what extent, if any, is there a difference in adult student achievement as measured by the WIAT-III between male and female students, and to what extent, if any, is there an interaction between learning method and gender on adult student achievement as measured by the WIAT-III? A 2-way between-subjects ANOVA was used to determine whether there were any statistically significant differences between the groups being examined. The findings rejected the null hypotheses for learning method F(1, 135) = 24.710, p = 0.000, partial [eta]2 = 0.155, gender F(1, 135) = 122.453, p = 0.000, partial [eta]2 = 0.476, and interaction F(1, 135) = 34.350, p = 0.000, partial [eta]2 = 0.203. These findings may be used to inform higher education institutions and leaders of best practices in creating learning methods that best meet the needs of all adult learners. [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.]