Half of all fish species school at some point during their lives, providing a range of benefits such as increased predator avoidance. Theory suggests that the defensive advantages of group-living are maximised when individuals exhibit homogeneity in a range of morphological characteristics such as body size and colouration. However, no one has yet tested whether gregarious fish species assort according to physiological characteristics like metabolism and whether this assorting affects the group’s escape behaviour. In this study, we collected 11 distinct wild schools of the damselfish Chromis viridis from shallow reefs surrounding Lizard Island in the northern Great Barrier Reef. The flow regimes for each collection site were measured on six random days over a three-week period. The metabolic rate (standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope (AS)) of eight random individuals from each school were measured using intermittent-flow respirometry. The group’s escape behaviour was then tested in a laminar flow swim tunnel, in which the school’s response to an aerial stimulus was recorded in high-speed (240 fps). We found evidence of assorting by metabolism within each of these schools, with greater similiarities found within schools than between schools. Schools with a higher aerobic scope exhibited more effective escape responses, with a faster latency time and greater turning rate in response to the stimulus. Though SMR was independent of flow rate, the other measures of metabolism (MMR and AS) and escape performance all increased in schools from a high-flow regime reef. These results suggest physiological assorting is occuring on the reef, though further studies are needed to determine if this is occuring due to passive or active mechanisms. This physiological similiarity among fish within a school has effects on the escape behaviour of the group, with escape performance improving with higher aerobic scope and flow in the school’s home reef.