80 preschool children were each administered 40 trials on a key-pressing apparatus. Marbles served as reinforcers. So given a ready signal performed faster than So not given a ready signal. There was no difference in the mean speeds of the partial reinforcement and the varied delay groups, but both of them performed faster than the constant delay group. The continuously and immediately rewarded group performed faster than the other three groups. The effect of a particular reward condition manifested itself on the immediately following trials. Interpretation in terms of competing responses was offered
