In addition to the following questions about TIMSS, more FAQs about international assessments are available at: http://nces.ed.gov/surveys/international/faqs.asp.
The seeming inconsistencies between the 2007 achievement scores of U.S. boys and girls in mathematics and science are not easily explainable. Research into differences in achievement by sex has been unable to offer any definitive explanation for these differences. For example, in examining sex differences primarily at the high school level Xie and Shauman (2003)1 found that "differences in mathematics and science achievement cannot be explained by the individual and familial influences that we examine." Indeed, that sex differences vary in the participating TIMSS countries some in favor of males and others in favor of females would appear to support the idea that the factors related to sex differences in mathematics and science achievement are complicated.
1Xie, Y. & Shauman, K. (2003). Women in Science: Career Processes and Outcomes. Boston, MA: Harvard University Press.