Two experiments were designed to assess children's ability to understand recursive structures of thinking which include thinking about contiguous people, thinking about action between people, thinking about thinking, and thinking about thinking about thinking. In Experiment I, 32 second, fourth, sixth, and eighth graders were tested on eight tasks designed to assess the ability to understand recursive structures. The tasks varied on both content and logical or structural dimensions. Both content and structure were found to have a significant effect on performance. In Experiment II, 24 concrete operational and 24 formal operational children, all eighth graders, were tested on nine recursive and noncursive tasks varying in content. A significant interaction was obtained between developmental level and structure of the task. Analyses indicated that formal operational subjects performed better than concrete operational subjects on the recursive tasks, while there was no difference in performance on two of the three nonrecursive tasks. The results were interpreted to support the hypotheses that the ability to understand recursive structure requires formal operations. (Author/MKM)