Teaching inquiry process is one of the most important objectives in science education. To promote students scientific process skills, a science teacher should encourage the students do something by themselves. One method for that purpose which has been used in many schools would be group experiment. The researcher has been experienced a lot of difficulties in controlling or guiding every group to finish the assigned experiment within the given class hour. Therefore, the researcher decided to select several leaders from students and trained them in advance of the given class hour. This leaders are expected to guide the remaining students in the class. As the result of this study, the classroom with and without student leaders showed very significant difference(P>0.001) in their achievement of scientific process skills. The experimental group also showed more positive attitude toward science. The researcher concluded that the use of student leaders is very effective in promoting scientific process skills. This method is also regarded very effective in a large class sized like Korean Schools.