Problem behaviors are prevalent in schools and may result in negative effects for the students exhibiting those behaviors, teachers, and other students. Increasing on-task behaviors has been shown to minimize disruptive behaviors. The current study utilized an interdependent group contingency-based intervention, Class-Wide Function-related Intervention Teams (CW-FIT), to increase on-task behavior in elementary classrooms. A concurrent multiple baseline design was used to examine the effects of CW-FIT during whole-group instruction for six at-risk students in three classrooms (kindergarten, first, and third grade). The study examined whether CW-FIT would: (1) increase on-task behaviors of students, (2), increase teacher praise and reduce teacher reprimands, (3) result in improved on-task behavior, praise, and reprimands during times of the day when CW-FIT was not implemented, and (4) increase attendance and classroom engagement, and decrease office discipline referrals. Results showed CW-FIT improved on-task behavior for five out of six at-risk students. The sixth student already demonstrated high on-task behavior before CW-FIT was implemented. Praise rates increased for all teachers, although praise rates decreased over time for two teachers. Few teacher reprimands were observed, so it was not possible to evaluate effects on CW-FIT on reprimands. Insufficient data were available to make strong conclusions on whether the effects of CW-FIT generalized to other parts of the day; however, there was some evidence that on-task behavior improved for at least one student from each classroom when CW-FIT was not being implemented. No significant differences were found in attendance rates before and after CW-FIT was implemented. Self-reported ratings of classroom engagement for all at-risk students improved after CW-FIT. No office discipline referrals were reported across classrooms. CW-FIT was well accepted by students and teachers. Overall, CW-FIT produced an increase in on-task behavior, teacher praise, improved student engagement in the classroom, and the effects may generalize to other parts of the day. [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.]