Background: This study was grounded in the differentiated instructional model where teachers tailor content, process/support, and product in response to their students' levels of readiness and interest. The value of differentiated teaching is well established; however, the implementation of such a technique is difficult due to differences in student skills and preferences. Purpose: In this study, we sought to explore physical education (PE) teachers' perceptions about the need for differentiation in their swimming programs (i.e. the differentiation "rhetoric"), along with their actual use of differentiation strategies (i.e. the differentiation "reality") in their swimming lessons. Participants: Three Western Australian high school Year 8 and Year 9 PE teachers (two from a non-government school and one from a government school), ranging in age from 25 to 39 years and with 5 to 15 years of PE teaching experience, participated in this study. The study involved four classes, totaling 103 students. Data collection: Teachers' perceptions about the need for differentiation, along with their actual use of differentiation strategies, were recorded using class observations (i.e. 36 lessons) and questionnaires and were supported by in-depth teacher interviews. Students from these classes were also targeted for observation and interview during a single school term. Data analysis: Observation data were inductively analyzed according to Tomlinson's model of differentiation. All interviews were tape-recorded and transcribed verbatim, before transcripts were coded in order to identify recurring themes. Percentage yes/no scores were calculated for student questionnaire data. Findings: While successfully differentiating content and process/support in the swimming classroom, teachers infrequently differentiated for product (e.g. different forms of assessment). Moreover, the limitations of space/numbers, time, and student readiness impacted on the differentiation strategies and student learning opportunities and outcomes. Conclusion: Implementing a differentiated approach to swimming teaching appears to represent a significant challenge, though these data provide evidence of differentiated pedagogy that facilitated student learning outcomes.