The present study aimed at analyzing the performance of Ss at various age levels in a two-choice task, and comparing these findings with those of other investigators who have utilized analogous tasks. 126 Ss, who were 4, 6, 10 or 20 years old, participated in the experiment. A procedure like Weir-type (1964) probabilistic experiment was undertaken. Two different reinforcement percentages for the payoff knob were used, 70% and 100%. Then on a 70% task a marble was delivered on 70% of the Ss' choices of the payoff knob, and then the 100% task was analogous to a so-called concept attainment task. The main point, which was different from the previous probabilistic problem-solving experiment, was the shift learning design employed.