Less than 50% of a PE lesson is usually spent in MVPA. A dependent-group contingency strategy, “Fair Play Game,” has shown effectiveness in increasing MVPA during PE lessons among students from affluent schools. The purpose of this study was to determine the effectiveness of this strategy on MVPA among students from an undeserved community. The Fair Play Game strategy consisted of goal setting, prompts, feedback, and rewards. A single-subject multiple baseline design was applied across two classes of students, throughout 15 soccer lessons. Three students from each class (N = 6) were selected for an individual analysis according to their MVPA level at baseline (low, medium, and high). Students wore a waist-mounted accelerometer during lessons. Students with a low level of MVPA at baseline from Year 8 presented a positive change in trend, level, and percentage of nonoverlapping MVPA data. The intervention was not effective to change MVPA for the other students. The Fair Play Game might be effective in increasing PA levels in students with low levels of activity from undeserved areas. However, the intervention needs to be tailored for each population and applied regularly for the benefits to be expanded to the whole class.