This investigation gives attention to the developmental course and influence of social class on self-directed, private speech. The Ss were 108 white, middle and lower class pre-school, first and third grade children. Two measures of receptive vocabulary were administered as background language measures. The experimental task required S to sort pictures of common objects into categories at three levels of task difficulty. The results indicated a rather marked decline in spontaneous verbalization from the pre-school to first grade levels with no significant change between the first and third grade levels. A parallel trend was found in the decreasing intensity level of the speech productions (i.e., a simultaneous decrease in overt vocalization and increase in silent lip-movement activity). These findings support Vygotsky's internalization hypothesis. A significant association was not found between the frequency of verbalization and problem solving performance, which casts doubt on the directive function of such verbal activity. Prominant social class differences in cognitive-linguistic abilities were also found. These differences may stem from the differential linguistic codes attributed to the middle and lower class patterns of verbal interaction. (Author/CJ)