In addition to the following questions about TIMSS, more FAQs about international assessments are available at: http://nces.ed.gov/surveys/international/faqs.asp.
Both TIMSS and NAEP provide a measure of fourth- and eighth-grade mathematics and science learning. It is natural to compare them, but the distinctions described below need to be kept in mind in understanding the converging or diverging results.
The most recent results from NAEP and TIMSS include information on trends over time in fourth- and eighth-grade mathematics achievement for a similar time interval: in NAEP between 1996 and 2011 and in TIMSS between 1995 and 2011.
Both assessments showed statistically significant increases in the mathematics performance of fourth- and eighth-grade students between these years.
The most recent results from TIMSS provide trend information for fourth- and eighth-grade science achievement between 1995 and 2011. In contrast, NAEP only provides trends for fourth-grade between 1996 and 2005 and for eighth-grade between 1996 and 2005 as well as between 2009 and 2011. (Due to a major revision of the NAEP Science Framework in 2009, no trend comparison can be made between 1996 and 2011). Compared with mathematics, the available trends shown by NAEP and TIMSS in science are less consistent with one another.
In fourth grade, NAEP shows that there was an increase in students' science performance overall between 1996 and 2005, whereas TIMSS did not detect any change in performance from 1995 to 2007. In eighth-grade, NAEP detected no measurable change between 1996 and 2005, but shows an increase in student's science performance overall between 2009 and 2011. In contrast, TIMSS detected an increase between 1995 and 2003 and between 1995 and 2011, but detected no measurable change between 2003 and 2011 or between 2007 and 2011.