As the largest international study ever taken in history, the Trend in Mathematics and Science Study (TIMSS) has been held as a benchmark to measure U.S. student performance in the global context. In-depth analyses of the TIMSS project are conducted in this study to examine key issues of the comparative investigation: (1) item flaws in mathematics and science; (2) inability to reflect item score differences between adjacent grades; (3) ambiguity of the test items behind nonrandom guessing; and (4) unfair comparisons resulted from inconsistent item difficulties across the nations. The TIMSS item checking could help education stakeholders understand more profound assessment issues through the information triangulation.