Robots evolve from tools to information media since they generates information by interacting with human. As studies on robot-aided education are still in a starting phase, attempts need to be made to use robots for educational purposes and to investigate the effects of the use. It was showed that robot-aided learning was friendlier than other media assisted learning, and especially effective for motivating children. We developed the prototype robot Jenny that can help teachers as a educational media in class(i.e. as a T.A. robot, it can present robot contents on its chest to screen and explain about it when teacher asks). is a schoolmate for 5th or 6th grade children or an elder schoolmate for the rest. We performed the field trial at an elementary school. We carried out 9 classes for three subjects(english, korean, music) with -students in $4th{sim}5th$ grade. They thought Jenny who was 13 years old as an elder schoolmate in 6th grade. Also, a significant difference was found in the interest and concentration of experimental groups from controlled groups.