Poll: I have a startup idea. How should I pursue it?

I've had an idea for a startup that has been kicking around the back of my mind since 2007 (that's when I created a Google Doc describing it in detail and registered a bunch of domain names for it). It is in the education sphere, and it seemed a little outlandish 5 years ago, but now that MOOC's are very common, it seems like an obvious evolution for online education. A little background...I am currently working as a software engineer for a stealth mode startup in the social/big data space, but over my career, I've worked for some big names in for-profit education (Sylvan, Kaplan, The College Network, Veritas Prep). The idea solves a problem for all of those companies, and for universities as well, so it could make a profitable startup but I think it could be more impactful with a WordPress-like model. How would you pursue an idea like this?