A quasi-experiment was carried out in a college success strategies course to evaluate the impact of structured interpersonal interaction on undergraduate students' Academic Engagement and Academic Achievement. The course, EPL 259: Individual Learning and Motivation, employs a blended learning instructional model that requires students to spend the majority of class time working independently on online activities. In the experiment, students in six treatment sections were exposed to some combination of two types of interpersonal interaction, categorized as Student-Student Interaction and Student-Instructor Interaction. Student-Student Interaction was facilitated in two different ways: (1) through in-class, cooperative learning activities, and (2) through online, asynchronous discussion board activities. Two sections of EPL 259 received the first Student-Student Interaction format, two sections received the second format, and two sections received neither format. In addition, in each of these three pairs of sections, one section also received Student-Instructor Interaction, facilitated through required, weekly, one-on-one meetings between each student and the instructor. Academic Engagement and Academic Achievement were each measured in two ways. Academic Engagement was measured: (1) through data on students' course-related behaviors, including rates of attendance, tardiness, submission of assignments, and late submission of papers, and (2) through students' scores on a multifactor survey of course engagement. Academic Achievement was measured: (1) through total points earned on online activities and papers, and (2) through grades on the final examination. A series of Analyses of Covariance (ANCOVAs), utilizing participants' Prior Cumulative GPA and measures of Conscientiousness and Extraversion as covariates, was carried out to assess treatment effects. Sections of the course that experienced Student- Student Interaction through in-class, cooperative learning activities displayed significantly higher Academic Engagement (measured through the multifactor survey) than sections that experienced either online, asynchronous discussions or no Student-Student Interaction whatsoever. Likewise, sections of the course that experienced Student-Instructor Interaction through weekly, one-on-one instructor meetings displayed significantly higher Academic Engagement than sections that experienced no Student-Instructor Interaction whatsoever. An interaction effect between Student-Student Interaction and Student-Instructor Interaction mediated the impact of both treatments on Academic Achievement (measured through final exam grade). In the absence of Student-Instructor Interaction, both forms of Student-Student Interaction (i.e. in-class and online) had a positive impact on Academic Achievement. However, when Student-Instructor Interaction was required, online Student-Student Interaction was observed to have a negative impact. Similarly, in the absence of Student-Student Interaction, required one-on-one instructor meetings were observed to have a positive impact on Academic Achievement. However, when online Student-Student Interaction was required, instructor meetings were observed to have a negative impact. [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.]