This investigation presents a comparative study between a classroom atmosphere conducive to inquiry, with teachers considered qualified for this type of teaching, and the more formal didactic lecture-demonstration type teaching (traditional), with teachers judged to be particularly competent in this approach. The sample consisted of 582 pupils from grades five through eight, enrolled in a physical science program. The investigation was organized and the data processed, using analysis of covariance techniques, in such a way that independent comparisons of the relative effectiveness of both programs could be determined at each grade level. Testing instruments included: Test on Understanding Science (TOUS); Test of Science Comprehension (Nelson and Mason); the Questest by Suchman; and the Stanford Achievement Test, Science, Form W, Intermediate II and Advanced Levels. Conclusions include: (1) students receiving inquiry training develop a significantly greater understanding of science and scientists, as well as greater fluency and productivity in using skills of inquiry or critical thinking; and (2) no consistent difference in content mastery or retention of knowledge of the usual content of elementary school science was found. (Author/EB)