The purpose of this study was to compare the acute physiological responses within and between resistance training (RT) and high intensity interval training (HIIT) matched for time and with comparable effort, in a school setting. Seventeen early adolescents (12.9 ± 0.3 y) performed both RT (2-5 repetitions perceived short of failure at the end of each set) and HIIT (90% of age predicted maximum heart rate), equated for total work set and recovery period durations comprising of 12 'sets' of 30 s work followed by 30 s recovery (total session time 12 min). Variables of interest included oxygen consumption, set and session heart rate (HR) and rate of perceived exertion (RPE), and change in salivary cortisol (SC), salivary alpha amylase (SαA), and blood lactate (BL) from pre- to post-session. Analyses were conducted to determine responses within and between the two different protocols. For both RT and HIIT there were very large increases pre- to post-trial for SC and BL, and only BL increased greater in HIIT (9.1 ± 2.6 mmol·L) than RT (6.8 ± 3.3 mmol·L). Mean set HR for both RT (170 ± 9.1 bpm) and HIIT (179 ± 5.6 bpm) was at least 85% of HR maximum. VO2 over all 12 sets was greater for HIIT (33.8 ± 5.21 mL·kg·min) than RT (24.9 ± 3.23 mL·kg·min). Brief, repetitive, intermittent forays into high, but not supra-maximal intensity exercise utilising either RT or HIIT appeared to be a potent physiological stimulus in adolescents.