In one of Professor Wu's recent lectures,
http://math.berkeley.edu/~wu/Lisbon2010_4.pdf
he points out a problem of fraction addition from the federal National Assessment of Educational Progress (NAEP) survey project. On page 39 of his presentation handout (numbered in the .PDF of his lecture notes as page 38), he shows the fraction addition problem
12/13 + 7/8
for which eighth grade students were not even required to give a numerically exact answer, but only an estimate of the correct answer to the nearest natural number from five answer choices, which were
(a) 1
(b) 19
(c) 21
(d) I don't know
(e) 2
The statistics from the federal test revealed that for their best estimate of the sum of 12/13 + 7/8,
7 percent of eighth-graders chose answer choice a, that is 1;
28 percent of eighth-graders chose answer choice b, that is 19;
27 percent of eighth-graders chose answer choice c, that is 21;
14 percent of eighth-graders chose answer choice d, that is "I don't know";
while
24 percent of eighth-graders chose answer choice e, that is 2 (the best estimate of the sum).
I told Richard Rusczyk of the Art of Problem Solving about Professor Wu's document by email, and he later commented to me that Professor Wu "buried the lead" (underemphasized the most interesting point) in his lecture by not starting out the lecture with that shocking fact. Rusczyk commented that that basically means roughly three-fourths of American young people have no chance of success in a science or technology career with that weak an understanding of fraction arithmetic.
Plenty of other mathematics teachers in the United States have noticed adult-age students who have trouble with elementary fraction arithmetic.
http://www.brianrude.com/fractionsquiz2.htm
Professor Wu has written other important articles about what needs to be reformed in United States mathematics education.
http://math.berkeley.edu/~wu/Lisbon2010_2.pdf
http://math.berkeley.edu/~wu/NCTM2010.pdf
http://math.berkeley.edu/~wu/NoticesAMS2011.pdf
http://math.berkeley.edu/~wu/CommonCoreIV.pdf
Other mathematicians who have written interesting articles about mathematics education reform in the United States include Richard Askey,
http://www.aft.org/pdfs/americaneducator/fall1999/amed1.pdf
http://www.math.wisc.edu/~askey/ask-gian.pdf
Roger E. Howe,
http://www.ams.org/notices/199908/rev-howe.pdf
Patricia Kenschaft,
http://www.ams.org/notices/200502/fea-kenschaft.pdf
and
James Milgram.
ftp://math.stanford.edu/pub/papers/milgram/milgram-msri.pdf
ftp://math.stanford.edu/pub/papers/milgram/report-on-cmp.html
All those mathematicians think that the United States could do much better than it does in teaching elementary mathematics in the public school system. Several of them identify lapses in teaching fraction arithmetic as a major issue. I think so too after living in Taiwan twice in my adult life (January 1982 through February 1985, and December 1998 through July 2001). Taiwan is not the only place where elementary mathematics instruction is better than it is in the United States. Chapter 1: "International Student Achievement in Mathematics" from the TIMSS 2007 study of mathematics achievement in many different countries includes, in Exhibit 1.1 (pages 34 and 35)
http://pirls.bc.edu/timss2007/PDF/T07_M_IR_Chapter1.pdf
a chart of mathematics achievement levels in various countries. Although the United States is above the international average score among the countries surveyed, as we would expect from the level of economic development in the United States, the United States is well below the top country listed, which is Singapore. An average United States student is at the bottom quartile level for Singapore, or from another point of view, a top quartile student in the United States is only at the level of an average student in Singapore. I've been curious about mathematics education in Singapore ever since I heard of these results from an earlier TIMSS sample in the 1990s. I have seen the textbooks used in Singapore (and have used those to teach my own children, including a grown child who is now a hacker) and own many of the textbooks used in Taiwan and China (as I read Chinese). The United States could plainly be doing better in elementary mathematics education.
The article "The Singaporean Mathematics Curriculum: Connections to TIMSS"
http://www.merga.net.au/documents/RP182006.pdf
by a Singaporean author explains some of the background to the Singapore mathematics materials and how they approach topics that are foundational for later mathematics study. I am amazed that persons from Singapore in my generation (born in the late 1950s) grew up in a country that was extremely poor (it's hard to remember that about Singapore, but until the 1970s Singapore was definitely part of the Third World) and were educated in a foreign language (the language of schooling in Singapore has long been English, but the home languages of most Singaporeans are south Chinese languages like my wife's native Hokkien or Austronesian languages like Malay or Indian languages like Tamil) and yet received very thorough instruction in mathematics. It would be good for the United States to take advantage of its greater degree of linguistic unity and childhood wealth to reach the educational standard of the top-performing countries in other parts of the world.