Public school leaders have searched for solutions to disruptive student behavior and its effect on academic concerns. As a result, research-based behavior models such as school-wide positive behavior support (SWPBS) were used to adjust student behavior with the goal of improving academic achievement; therefore, there is a necessity to understand if participation in this program does in fact impact student achievement. This study was an examination of the difference in reading academic achievement of third grade students who participated in School-Wide Positive Behavior Support program (SWPBS), compared to those who did not. The reading achievement examined in this causal comparative ex-post facto study was measured by Florida's reading proficiency scores, as measured by Grade 3 Florida Standards Assessment English Language Arts paper-based test. The data reviewed third grade students in 277 schools in one South Florida public school district. Descriptive statistics were used to find the mean of reading academic proficiency scores for third grade students in school-wide positive behavior support schools compared to those who were not. A t test for independence was then used to compare the means of the students' reading proficiency scores in SWPBS schools and those who were not. The data examined third grade students' reading academic achievement in three groupings; with all schools, in schools not designated as the lowest 300, and in schools designated as the lowest 300. The data was then desegregated to examine third grade students' reading academic achievement in individual reading proficiency levels for schools participating in SWPBS compared to those who were not. Results indicated no difference in reading academic achievement for schools participating in SWPBS compared to those that did not.