U.s. Educational System Ranking

[Moghedien]

america has received scores around 500 on a scale that goes up to 1,000: 487 in math, 500 in reading and 502 in science.
The three-yearly OECD Programme for International Student Assessment (PISA) report, which compares the knowledge and skills of 15-year-olds in 70 countries around the world, ranked the United States 14th out of 34 OECD countries for reading skills, 17th for science and a below-average 25th for mathematics.



According to the U.S. Department of Education?s 2007 ?Trends in International Mathematics and Science Study? (TIMSS), the U.S. trails behind the following countries in average mathematics scores:

Singapore
Taiwan
Japan
Republic of Korea
Hong Kong
Sweden
Netherlands
Hungary
Slovenia

Now overall by several organizations have rated the United States 23 overall in Education.
Why is the American Education System so lacking. During the Cold War we were Always in the top 3 usually number 1. What changed? IS it a cultural difference? Political?

(When i have kids im seriously considering sending them to the Japanese Educational System which is far more rigorous.)