This paper shows how gender, science, and assessment are all built on a fundamental set of dualistic concepts associated with masculine power and privilege. It also shows that a manageable change to curriculum, instruction, and assessment practices, moving from the conventional masculine paradigm of "quality" practice to a reconstructed perspective incorporating the feminine side of the dualisms, has an immediate and dramatic impact on historical achievement profiles. In this study, about 5,000 physics students in grade 12 in Victoria (Australia), have undertaken new assessment processes in physics for university selection, and it has been found that girls have suddenly become brilliant at physics. Changing assessment protocols has an immediate impact on the success of girls in physics. This pattern has been retained over a 5-year period with the new curriculum and assessment practices, and it follows a 20-year plus period when it was assumed that boys were just "naturally" better at physics than girls. Tools from post-structural feminism are used to explore "both/and" notions - in lieu of common "either/or" conceptions - of the gendered binaries that underpin assessment, and hence to reconstruct and explain this positive effect on achievement profiles. (Contains 2 tables and 68 references.) (Author/SLD)