The Trends in Mathematics and Science Study (TIMSS) is a time-series database, which provides an early warning for necessary curricular reforms in mathematics and science subjects and offers an opportunity for schools and policymakers to reflect on the effectiveness of educational changes. It provides vital data for governments and researchers to compare and contrast differences in students' mathematics performance within and between countries. Chinese Taipei's Ministry of Education (MOE) has used successive cycles of TIMSS data as a guide for formulating educational policies, and an evidence base for evaluating their effects. Although Taiwanese students have performed well in TIMSS, the percentage of students reporting low confidence in and low enjoyment of mathematics is significantly greater than the international average. This article examines the strong connection between TIMSS and mathematics education reform in Chinese Taipei, showing how the TIMSS 2003 results (Mullis et al., 2004) led the MOE to develop the 2006 "After Class Support" policy and the subsequent TIMSS data-inspired Just Do Math program, a new approach to mathematics teaching and learning introduced in 2014.