Pros
The company is still rapidly growing and they like to promote from within. So if you are passionate about the business side of K-12 education and willing to relocate, you can find yourself moving up the ranks very quickly.
Cons
The expectation of middle management and above is to basically be available 24-7. It's not unheard of to wake up in the morning and see that email conversations were happening after midnight and decisions were being made without your input. Personally, with a family at home that was a little much for me. Also, philosophically many have issues with the charter school movement and K12 profits greatly in areas that are struggling for funding. They can paint it any way they want, but when it comes down to it K12 Inc. receives millions in funding through public revenue sources, and then as a private entity they will focus first and foremost on making a profit rather than serving their students.