Eighty-four Grade 1 boys were randomly assigned to 1 of 12 experimental or two control conditions. Experimental subjects were trained under one of six punishment conditions, varying in respect to intensity of punishment, timing of punishment, and cognitive structure. Results indicated that when cognitive structure was low, response inhibition was stronger after early, than after late punishment and that high-intensity punishment was a more effective inhibitor than low-intensity punishment. The provision of highcognitive structure was very effective for inducing response inhibition, especially when punishment was delivered late. Telemetered heart-rate data secured throughout the experiment further support the suggestion that, under certain conditions, response inhibition may be produced primarily by emotional arousal, and, under other conditions, by the availability of prohibition rules. © 1969.