http://learninfreedom.org/age_grading_bad.html
and indeed my mother must have learned that way in the rural one-room school for grades 1 through 8 that she attended during the Great Depression. It's good that now pervasive technology is helping teachers relearn that children who occupy the same classroom don't all have to literally be "on the same page" at the same time. That allows more able (or more motivated) learners to move ahead of the meager expectations of the United States curriculum,
http://educationnext.org/teaching-math-to-the-talented/
an improvement that is long overdue.
"Critics argue that Khan’s videos and software encourage uncreative, repetitive drilling."
I agree that the Khan Academy exercises currently are just that, exercises, and have suggested here on HN that the Khan Academy exercise writers do the hard work of building genuine online problem sets.
http://news.ycombinator.com/item?id=2760663
Fixing the nature of the online exercises and turning them more into problems would help with one defect noted in the article: "Of course, kids who’ve grown up on computers are quick to spot the weaknesses in Khan’s system. They discovered ways to cheat on the drills: In the logarithms unit, for example, they noticed that the third multiple-choice answer was always the right one." But as the article points out throughout, what online reporting and pratice has allowed is for children who are already attending school anyhow to use their class time to discuss what are actual PROBLEMS for each learner, with interaction with a live teacher, saving drill for times of the day when the teacher is not available. That's not a bad improvement at all.
I should mention that in my own family we spend money on the ALEKS program
for our homeschooled children, and we find that very helpful. It has many of the same strengths of the Khan Academy program (but is not free, nor does it have audio explanations) with a more complete syllabus and more challenging problems. The "knowledge spaces" theory underlying ALEKS
http://www.aleks.com/about_aleks/Science_Behind_ALEKS.pdf
is quite interesting and will probably have to be reflected by any complete K-12 mathematics program anywhere in the world. None of our children actively enjoy ALEKS, but they acknowledge that it is helpful for learning math, and I teach about the more cool aspects of math in the in-person math classes I teach through my local nonprofit organization.