This study developed an empirically based questionnaire to monitor young learners' conceptions of nature of science (NOS). The questionnaire, entitled Students' Ideas about Nature of Science (SINOS), measured views on theory-ladenness, use of creativity and imagination, tentativeness of scientific knowledge, durability of scientific knowledge, coherence and objectivity in science, the science for girls stereotype, and the science for boys stereotype. SINOS was constructed based on the written responses of 431 sixth graders, elementary students' quotations in theses and books related to NOS, and student interviews. The draft questionnaire was administered to 1,139 third to sixth graders (aged 9-12) in Taiwan. According to the results of an item analysis, and reliability and validity tests, 47 out of 62 items were selected for the current version. It was further validated by a sample of 1,091 5th and 6th graders. Confirmatory factor analysis revealed that all of the 5th graders, 6th graders, girls, and boys' data could be explained by the 7-factor structure. The overall reliability as measured by Cronbach's alpha was 0.85. The relations between the SINOS scores and the achievement scores are presented. The instrument yields valid and reliable data useful for inferential statistics, and allows researchers and educators to relate NOS views to other measurable educational outcomes. (Contains 4 tables.)