Please for the love of maths do not "align" with the common core standards. It would be the saddest, most disheartening thing imaginable* for Khan Academy to become a feeder to the American standardized testing system. The author writes: "If one of Khan Academy’s goals is to prepare students for success in Common Core mathematics, they’re emphasizing the wrong set of skills." I would like nothing better than the acad…
Now, if you believe the curriculum is poorly designed or the test is poorly correlated with it, I encourage you to make that argument. But explaining why "Know relative sizes of measurement units within one system of units including km, m, cm..." should not be part of the curriculum is a lot harder than making emotional pleas about "love of the subject".
(I've skimmed parts of the common core on a few occasions. It looks pretty good to me. http://www.corestandards.org/Math/Content/4/MD/ )