Sex differences in performance of year-11 British students in science are being explored in an ongoing study. Some early results and tentative conclusions are reported. Double award science was introduced in England to improve scientific literacy, to reduce sex imbalances in later science pursuits by females, and to encourage generally greater pursuit of science in further and higher education. This paper considers the results for the Nuffield Syllabus Coordinated Sciences Double Award (1772) tests for 1996, focusing on how teaching combined sciences has influenced sex differences. These results are considered in light of the National Curriculum and the changes in public examinations in the British system. Results are considered for 13,969 females and 13,957 males for the 4 components of the Nuffield examinations. These students were all candidates for the next tier of education, so that they might represent the most able portion of the total student cohort. Analysis of these results indicates that the sex gap favoring males in performance in physics has been masked by the introduction of the double science public examination. Results suggest that the traditional pattern of sex differences still exists, and further research is required to investigate the relatively weaker performance of female students on specific types of items. (Contains 13 figures, 11 tables, and 128 references.) (SLD)