Kindergarten and first-grade children participated in a study of the role of reciprocal and inversion reversibility in language acquisition and cognitive development. Subjects completed cognitive tasks assessing conservation, seriation, and class inclusion, and language tasks assessing the active-passive transformation and the negative transformation. Results confirmed the hypothesis that reciprocal reversibility is demonstrated simultaneously in the active-passive transformation, seriation, and conservation. Children, however, did not demonstrate inversion reversibility in their performance on negation, class inclusion, or conservation. For the group as a whole, the order of difficulty for the tasks, from most difficult to easiest, was as follows: class inclusion, conservation, seriation, active-passive, and negation. When task scores were separated into high, medium, and low categories, both negation and active-passive were significantly ordered in relation to each of the cognitive tasks. (Author/AA)