Heart rate (HR) monitoring during exercise represents a potentially useful strategy for teachers delivering physical education lessons. This study examined how projecting HR monitor data onto a screen acutely affected school students’ exercise intensity during a high-intensity interval training (HIIT) session. Twenty students (12.3 ± 0.9 years, male = 8, female = 12) from one primary school volunteered to participate. Using a randomised crossover design within a 4-week period, participants completed four sessions of HIIT with HR projection and four sessions of HIIT with no ability to view HR. During the HR projection condition all participants viewed their HR on a class screen in real-time, with a changing colour according to HR level. Target intensity was 90% of age-predicted maximum HR. Peak HR and time above 90% HR (RED) were collected in all sessions. Student focus groups and teacher interviews were conducted to gain perceptions around the effects of the projection. Peak HR (p = 0.005, η2 effect size = 0.049) and RED (p = 0.000, η2 effect size = 0.083) were significantly greater during the projected condition. Qualitative data indicated that projection improved student motivation to reach the target, and ignited competition amongst peers to work harder. Projecting HR data onto a screen can increase the acute exercise intensity of school students during HIIT. HR projection therefore represents a useful strategy for the delivery of exercise sessions with an emphasis on intensity, within physical education classes.