The purpose of this study was to examine teachers' competency in teaching for student competence in science. Drawing on literature on competence and science teacher education, we identified 44 indicators of science teaching competence in relation to the current Korean National Science Curriculum, from which 54 items for teachers' self-assessment were developed and validated. Through online administration of the self-assessment instrument, responses from 210 primary and secondary teachers were collected. Factor analysis resulted in nine factors across three competence areas. Teacher competence differed across factors. One-way ANOVA analysis revealed that primary teachers indicated significantly higher competence in most aspects of teaching than secondary teachers and that years of teaching was related to professional development methods utilized by teachers. Suggestions for professional development program design and further research topics were discussed.