Research on social skills in physical education has shown that students' fair play behaviors often remain underdeveloped unless teachers include social skills' development into curriculum and instruction (Giebink & McKenzie, 1985; Siedentop, Hastie, & van der Mars, 2004; Vidoni, 2005). Fair play behaviors are learned behaviors that are specific to the context of physical education and sport. One approach that may guide a student in social interactions without drifting from a focus on learning tasks is to integrate the teaching of fair play concepts into the instruction. The purpose of this study was to examine the effects of Fair Play Instruction on two 8th-grade middle school classes. A multiple baseline design across two behaviors was used to assess the effects of Fair Play Instruction on: (a) students' active participation, and (b) students' helpful, harmful, and missed behaviors during a tag rugby unit. The Fair Play Instruction consisted of: (a) students' developing a chart with fair play cues to be accomplished during the lesson, (b) teacher's prompts and praise during the lesson related to fair play behaviors, and (c) positive pinpointing of fair play behaviors used by students during the lesson closure. Social validity questionnaires assessing the acceptability of the intervention's goals, procedures, and outcomes were completed by students, the teacher, and a panel of physical education professionals. Results showed that the Fair Play Instruction was consistently effective in increasing students' active participation, and in decreasing waiting time for all participants. The Fair Play Instruction for helpful behaviors was not implemented in the same manner as the instruction for effort, and there was little difference between baseline and intervention for helpful behaviors. There was, however, a decrease in the number of harmful behaviors. The primary explanation for the difference in effects between the effort behaviors and the helpful behaviors was attributed to the frequency of prompts and praise. During the intervention for effort behaviors the teacher increased her frequency of prompting and praising substantially over baseline. This was not the case for helpful behaviors. The social validity questionnaire showed that Fair Play Instruction was considered as an acceptable pedagogy among the students, the teacher, and a panel of physical education professionals. Although further investigation is needed, this study shows that Fair Play Instruction is a promising path to pursue the teaching of social skills in physical education.Keyword(s): middle school issues, physical activity, violence/prevention