In this study, the authors examined the effects of a systematic functional assessment-based intervention (FABI) to identify the function of a third-grade student's off-task behavior and create a plan to increase academic engaged time (AET). The FABI was designed and implemented in an urban elementary school with a comprehensive, integrated, three-tiered (CI3T) model of prevention. In Fall 2009, Ms. Adams, Caleb's general education teacher, nominated him for support through Project FUNCTION because of his distractibility, off-task behavior, and poor grades. When Ms. Adams requested Project FUNCTION supports, Caleb was beginning the referral process for special education; however, he did not receive special education services during this intervention. After obtaining teacher and parent consent and student assent, four graduate students (liaisons) collaborated with Ms. Adams to design, implement, and evaluate Caleb's FABI over a 7-week period. In this article, the authors describe how the liaisons worked with Ms. Adams and Caleb to design, implement, and evaluate the FABI, including: (1) steps taken to gather data for the functional assessment; (2) how the Function Matrix was used to analyze functional assessment data and hypothesize the function of Caleb's off-task behavior; and (3) how the appropriate intervention methods were selected using the Function-Based Intervention Decision Model. An intervention with both academic and behavioral components was developed and implemented to increase Caleb's AET. Additionally, the authors discuss the practical applications and feasibility of implementing the FABI within general education elementary classrooms. (Contains 6 tables and 2 figures.)