The purpose of this mixed-methods case study is to analyze the engagement levels of low-achieving high school seniors enrolled in a basic algebra course called Pre-College Algebra. The term low-achieving pertains to the class member participants enrolled in a course that is perceived and even described as the less rigorous of the choices of all fourth-year math courses. The course curriculum is indeed aligned with the most basic of algebra concepts - many of them aligning with sixth and seventh-grade concepts. However, students who enrolled in Pre-College Algebra experienced a change from teacher-centered pedagogies to student-centered heutagogy augmented by technology and influenced by developing a self-determined mindset towards learning. During a period of two academic semesters, students proceeded through an online modularized line of instruction activated through a subscription-based service that provides instruction aligned with a chosen textbook. Students took a pre- and post-survey and responded to items pertaining to engagement. The cross-survey results indicate changes in engagement of four types (known as engagement dimensions): behavioral, emotional/affective, cognitive, and social. To complement the survey results, students were asked five questions that were designed to elicit replies pertaining to their levels of satisfaction with the online modularized format. The replies to this questionnaire were analyzed in conjecture with noted observations of classroom occurrences. Student engagement was found to be influenced by the design and ensuing dynamics of an online modularized line of mathematics instruction. Statistically significant changes in engagement were found to be in the behavioral dimension.