In an attempt to devise a methodology for characterizing children's intuitive theories of drug action, 217 children in Grades 1 to 6 were interviewed about how two substances, alcohol and cocaine, cause behavioral changes in their users. Measures tapped both structure (Piagetian complexity of causal reasoning, coherence, and construction of a causal explanatory framework with nodes, links, and causal mechanisms) and content (a relevant biological ontology, mastery of propositions in a scientifically correct theory of drug action, and reliance on alternative theoretical models). Scores on all measures increased with age, especially between first and second grade and third and fourth grade. Growth between third/fourth and fifth/sixth grades was more evident for cocaine, the less familiar of the two substances. Measures of structure and content were correlated. Overall, elementary school age children appear capable of framing causal explanations of drug action and possess relevant biological knowledge, particularly about the central role of the brain in mediating the effects of drugs on behavior. It remains to be seen whether programs guided by an intuitive theories perspective and designed to increase children's understandings of how drugs alter behavior can contribute meaningfully to drug prevention efforts. (Contains 4 tables and 1 figure.)