AbstractExplaining natural phenomena is an important goal in science teaching. A logical analysis reveals that causal explanations exhibit formal operational structures in that they consist of implication statements chained together through transitive reasoning. It was hypothesized in the present study that individuals who do not reason formally will have difficulty in learning explanations presented in instruction. To test this hypothesis, the effect of levels of operational thought on the explanations which ninth‐grade (n = 26) and college (n = 40) physical science students reconstructed after instruction was investigated. Subjects in the study were classified through Piagetian tests as concrete or formal operational. Both concrete and formal subjects were successful in recalling explanations requiring the chaining of two implication statements. Formal operational subjects performed significantly better than concrete operational subjects in three of the four tests of the reconstruction of complex explanations requiring the chaining of six implication statements. In teaching complex causal explanations to students at the concrete operational level, it is suggested that teachers be prepared to furnish some external structuring which the students can rely on in logically relating the various propositions of the explanation to one another.