This video is directed at open source creators, but lots of points in here are applicable to education. Key points: What drives behavior (from most to least engaging):  status, access, power, stuff.  (Note "stuff", which costs the provider money, is last on the list!) The first minute of engagement is what determines what users think of your product.  Make the first step impossible to mess up!  Motivate users with a "Yay, you're awesome!" moment right away.  

Good summary of gaming in education to share with the uninitiated.