The effectiveness of microteaching techniques for improving presentation of science demonstrations by perspective science teachers was investigated. Three groups of students of ten members each were randomly selected from professional education courses for science teachers. Group A students presented two trials of two different demonstrations. Each presentation was video-taped and replayed immediately for the student making the presentation. Students in the micro-class verbally critiqued each presentation, evaluation it by means of an instrument developed for the study. Group B students were participants in four or more classes but did not perform demonstrations. Those in Group C were not involved in the microteaching experiences. The following quarter each student in Groups A, B, and C were evaluated while presenting demonstrations to classes in their secondary school practice teaching assignments. Results showed more increase in effectiveness between the first and second trials of the second demonstration than between the first and second trials of the first demonstration in the micro-class. It was also concluded that students who were members of the micro-classes presented better demonstrations when teaching than those who taught micro-classes. (DH)