Teachers tend to teach using the same methods that were in existence when they were children themselves. Called "social transmission of acquired behavior", scientists have shown this to be common among most species. In humans, it probably explains the monolithic inertia so evident in public education.
So when I started teaching math, I used worksheets, time tests, and rote memorization - all the same tools that had not worked when I was a child! What else did I know?
On March 27, 2004, (yes, I remember the date!) I met Corrinne Lieu, an experienced teacher from Singapore who had come to California after her marriage, and all that was soon to change.
Singapore math is, of course, the national curriculum of Singapore, and over the last ten years, it has been spreading gradually through progressive schools and districts across the US. (Editor's Note: Singapore historically ranks #1 or #2 in Math internationally, well ahead of the U.S. See related story here.)