Hi Lea, our Help desk team is much too small for telephone support, but let's see how we can reply here. As you probably know already Khan Academy is not an accredited school. It is a study aid. There are no way to automatically grade students based on what they do on the site either for most subjects. Teachers and parents are encouraged to test the student's knowledge in normal pen-and-paper tests (probably with calculator and perhaps compass etc. for your son) to eliminate the chance of cheating, or the possibility that the student has received an identical question recently.

The SAT material is different in that there is cooperation with the College Board, and students can take tests online and have their paper marked. Unfortunately there is currently a glitch which the College Board is hoping to fix soon with the grading.

I know different schools and different counties may have different rules about what kind of documentation they accept for his schooling. To be on the safe side should document his progress regularly with the downloadable report and by other means, and it may be necessary to take tests in an accredited setting at least once a year - but the school administration on a state level ought to be able to tell you how to go about it.

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Lea,  

Our local magnet high school has kids take the mid term and the final in one sitting in order to skip a class such as Algebra 2/Trig or calculus. Colleges seem to have you take a math placement exam once you are in.  If they are closed minded little helps.  If they are open minded a printout of his having mastered ALL of Kahn's math from Algebra through pre-calc etc. will help.  If he has skipped around they'll be concerned about "swiss cheese learning" because those gaps will burn you.

One summer my son studied on his own and almost passed.  He was frustrated that they made him retake the class, but in the end he realized they were right.   The next summer he took an online class in calculus and passed.  He'll finish 4 years of calculus in high school.  

I can't emphasize enough how important it is for your son to try and cover ALL of the subjects in succession, as both of my mathematician parents also encouraged him.  College may easily make him retake much of the calculus, especially from AP Calc BC on because the implications of how they apply the math is much more subtle as well. That is okay because those classes will be easier for him.  Might try some gifted courses such as Johns Hopkins Center for Talented youth http://cty.jhu.edu/  or your local community college in math.  

Socially it helps when they can still be with other kids their age, but with similar abilities and interests, as both of my parents advised after they each skipped grades  They encouraged me to find other ways to challenge them.  We also started some local STEM programs  and I tried to share what I've learned about math tracking and what has worked for us to build STEM in our community on my own site www.stemshoots.com/math-track   Best of Luck!