This paper briefly reports on a series of studies that explore the relationship between symbolic or pretend modes of reasoning and cognitive processes which underlie conservation of quantity. It is hypothesized that the mental transformations which the child makes while playing a game of make-believe, namely, the transformation from his original identity to a pretend identity and back to the original and enduring identity, are evidence of a primitive form of reversible thought operation and that this form of reversibility is akin to the reversibility that characterizes concrete operational thought. This hypothesized link was investigated by studying the effects of training in pretend play on performance on the conservation problem with preschool children. Five studies were conducted to address the following research questions: (1) the effectiveness of pretend play plus verbal inquiry training, (2) the comparative effectiveness of pretend play training vs. pretend play plus verbal inquiry training, and duration of these effects; (3) the comparative effectiveness of pretend play vs. direct conservation training vs. pretend play plus conservation training; (4) the comparative effectiveness of the adult initiated play approach vs. an approach in which the child teaches the adult; and (5) the comparative effectiveness of pretend play training vs. direct conservation training with low income children. A brief description of the methods and results of each study is provided. (SS)