According to Geekwire, "Digital Promise" is a new teaching initiative being launched by the U.S. Department of Education to push electronic teaching methods into schools. One of the partners in this enterprise is, surprisingly, Valve Software and the tool they're using to teach is Portal 2 and its Puzzle Creator.
More details can be found on the official Teaching With Portals website. Schools who are participating in the programme get access to special Steam accounts with all non-essential components removed through which they can use Portal 2 and the Portal 2 Puzzle Maker. All of this is available to the schools for free.
Lesson plans are freely available on the website to teach things like parabolas and simple harmonic motion. Currently only lesson plans for physics and maths are available but there seem to be unused categories for other subjects like chemistry and game design.
You can see the Teaching With Portals website here.