Teaching is not just about practicing the theory as it is. It requires the practical knowledge of the teacher to apply, alter and practice the theory in accordance with learners and class situations. To this end, the teacher is required to have the ability to comprehensively view affective aspects such as achievement motivation, class attitudes, and actual class situations, as well as have practical knowledge and reflective thoughts about classes. Therefore, the value of reflection which demands the change of behaviors through reflective thinking in teacher education is relighted and actively discussed. With sincere reflection, teachers are able to create and practice new knowledge by analyzing phenomena from a critical point of view that the value and knowledge that they believe to be absolute might not be true. Especially in science, where there is no absolute answer, the reflective process of continuously seeking answers is more important. Therefore, this study is intended to examine pre-service early childhood teacher s experience of reflection on the classes they teach to practice science classes in the kindergarten and the implications of reflection. To this end, 25 pre-service teachers, who were taking Early Childhood Science Education course intended for the third grade students, the Department of Early Childhood Education at K University, participated for 16 weeks in various activities such as writing journals, lesson planning for science teaching, group discussion, mock class and work experience. The collected data included teacher interviews, researchers’ field notes, ore-service teachers’ journals, and other related information. The results of this study indicated that open-mindedness and PCK are required prior to self-reflection, and that the practice of emulating the existing framework and intervention at an appropriate time are effective. The pre-service teachers’s experience of reflection on class is meaningful in that it can improves a sense of accomplishment and self-confidence, motivate them in teaching profession, and let them display collective intelligence in the learning community.