Math for hackers.
thirdstation: Allowing your site's users to create and share their own graphs through the content would be a useful tool.People absorb concepts differently so you won't know beforehand the best way to present the material.  This feature would allow say, another experienced math teacher, to create their version of the best journey through Mathematics.You can then keep track of the most popular graphs (through voting or usage).This feature would also help with your "but where then?" question.  If a graph creator thinks "basic number theory" should go between fractions and algebra but, there's no article about "basic number theory" then just putting it into their graph will create a stub article.Keeping track of stub articles would then let you know what topics are needed the most.Can't wait to see what you come up with.