The objective of this study was to develop an instrument to measure school students' competence in learning science as part of a large research project in Taiwan. The instrument consisted of 29 self-report, Likert-type items divided into 2 scales: Competence in Scientific Inquiry and Competence in Communication. The Competence in Scientific Inquiry scale contained 4 subscales: presenting questions and hypothesis, planning, experimenting and data gathering, and data analyzing, interpreting, and concluding. The Competence in Communication scale contained 4 subscales: expressing, evaluating, responding, and negotiating. Students were recruited randomly from primary, junior, and senior high schools in different regions of Taiwan to validate the instrument and establish its reliability and validity. The results of the analyses indicate that the instrument, scales, and subscales have reasonable internal consistency; that the theoretical structure was supported by empirical data; and that the subscales are homogeneous. These results indicate that it is an appropriate tool for measuring students' competence in learning science. Implications and suggestions for further studies are included. (Contains 2 tables and 1 figure.)