The success of an inservice program was evaluated by comparing and analyzing the results of tests administered to 11 participating (experimental group) and 15 non-participating (reference group) science teachers. Data on the improvement of preparation of the participants were obtained from the results of the Test on Understanding Science, a specially designed Test on the Historical Development of Science, and the Facts About Science Test. Results showed significant gains, by participants, in their understanding of the historical development of science relative to course topics and the methods and aims of science. These gains were found unrelated to total teaching experience, total teaching experience in the same subject(s) taught, undergraduate major, or previous inservice participation. Teachers showed a marked increase in their appreciation of the potential of the historical approach for science teaching. The availability of more such institutes with greater numbers participating is recommended. (BC)