ColinWright (the submitter of the blog post submitted here) is a mathematician who is evidently quite interested in effective mathematics education. This is far from the first Sunday in the United States when I have logged on to Hacker News to see a lively discussion of mathematics education sparked by one of Colin's posts.

I teach decimal arithmetic to third-, fourth-, and fifth-grade age pupils through my local nonprofit supplementary mathematics education program. My program uses the Prealgebra textbook published by the Art of Problem Solving foundation

http://www.artofproblemsolving.com/Store/viewitem.php?item=p...

and I encourage all the children in my classes not only to use the textbook problems and additional problems I assign in class, but also to view Richard Rusczyk's thought-provoking and FUNNY video lectures that go with the course lessons.

http://www.artofproblemsolving.com/Videos/index.php?type=pre...

To the specific point of the submitted blog post, the Art of Problem Solving (AoPS) lessons teach decimal numbers with varying numbers of decimal places and how to compare them and how to do arithmetic with them quite thoroughly. Anyone on the whole planet with an Internet video connection can watch the Art of Problem Solving video series for free, and even many fully grown adults with university educations could learn some new mathematics from some of the prealgebra videos (which are designed with child viewers of a young age in mind). I like the Art of Problem Solving videos and books a lot.

The Khan Academy developers, two of whom have already replied in this thread as I type this, are very responsive to the concerns expressed by outside observers on the quality of the lectures and especially on the quality of the online problems served up by the Khan Academy program. I have had specific individual email contact with one of Khan Academy developers after a comment of mine to Hacker News about Khan Academy a couple years ago. They are still iterating to make the Khan Academy program better. My third son is of age to begin eighth grade this autumn and has used many Khan Academy videos and online exercises to learn an impressive amount of mathematics and other science topics. We don't sole-source for ANY subject: we always use other materials for mathematics, and we always use other materials for all core academic subjects. (We are a homeschooling family of four children, one now grown up and working as a hacker for a startup.)

The open letter blog post kindly submitted here by Colin specifically mentions the Rational Number Project

http://www.cehd.umn.edu/ci/rationalnumberproject/

at my alma mater (the University of Minnesota), which consumed a lot of federal educational research funding for a long time. I regret that my university is associated with that project. The amount of PRACTICAL, ACTIONABLE, teacher-friendly lesson content that has come out of the Rational Number Project is tiny. Some of the leading mathematicians who write about mathematics education reform suggest better approaches for revising elementary school lessons on mathematics than that project has thus far suggested. For more background, see

http://mathforum.org/kb/message.jspa?messageID=6935384

http://math.berkeley.edu/~wu/NMPfractions4.pdf

Simply put, there are better examples of best practice in teaching decimal numbers to elementary school pupils in several countries of east Asia or southeast Asia or eastern Europe. We don't have to reinvent the wheel here, we just have to encourage the English-speaking mathematics educators to find the best materials used already in English (for example the AoPS materials and the standard school textbooks used in Singapore

http://www.singaporemath.com/Primary_Math_s/21.htm

and some mathematics contest-preparation materials) or to translate into English materials from Russia, China, Hungary, or Japan.

Meanwhile, I'm sure Khan Academy will keep iterating to improve, and will continue to be free to use. You can already shop around as a parent. There is no crisis here. But the discussion is interesting, and I thank Colin once again for an interesting weekend post on mathematics education.

P.S. I am on staff at Epsilon Camp

http://www.epsiloncamp.org/

this week, as I have been for the last week, so I've had opportunity to make acquaintance with some impressive young mathematics-liking children learning challenging mathematics. Some young people understand decimal arithmetic at quite an early age and need a way to move on beyond the slow pace of the school standard curriculum.