Normal children of the 2nd grade in elementary schools and mental retardates of comparable MA were administered tasks to learn finger mazes with two alternatives at each of nine choice points. At each choice point there was one of two kinds of texture and the textures were set to connect with correct positions. A half of the subjects was asked to verbalize the texture at each choice point. The verbalization facilitated the learning in a great degree, that is, increasing number of subjects who learned successfully the tasks not by memory but by conceptual thinking. Besides, the verbalization made longer response times. These findings suggest that the verbalization forced to change the style of cognitive behavior from impulsivity to reflection. These effects of verbalization were relatively strong for the mentally retarded children.