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 FAQs on how TIMSS compares to PISA and NAEP specifically provide a brief explanation of the differences between the assessments. To learn more about how the TIMSS assessment differs from PISA and NAEP, see the following papers:
Comparing TIMSS with NAEP and PISA in Mathematics and Science (2007) (281 KB)
Comparison of TIMSS 2011 Items and the NAEP 2011 Framework (2011) (756 KB)