From factory workers to Wall Street bankers, a reasonable proficiency in math is a crucial requirement for most well-paying jobs in a modern economy. Yet, over the past 30 years, mathematics achievement of US high school students has remained stagnant -- and significantly behind many other countries, including China, Japan, Finland, the Netherlands and Canada. A research team led by Carnegie Mellon University's Robert Siegler has identified a major source of the gap -- US students' inadequate knowledge of fractions and division.