Pros
K12 produces good courses that benefit many students; there's a shared sense of pride in the final product. Also, many interesting, talented people work there, and it's nice to count them among your colleagues. And it's fun to use technology to help students learn in a different way.
Cons
K12 has little loyalty to employees, even less to contractors. The company uses contractors extensively. (Top management is very concerned with how head count looks to investors and analysts.) Contractors are seldom converted to permanent staff, and they are subject to periods of no work. There's a lot of turnover, both among contractors and permanent staff. There is little hope for advancement in most positions. The CEO micromanages; senior management's hands are tied. They are aware of the problems but cannot do much to help. The brutal schedules and the race to stay ahead of students in new courses are exhausting to workers. If this was balanced by professional development, it would be easier to take. If you're hoping to build your career, there are better places to do so.