There really aren't a lot of books on XNA available yet (though some are coming) and real textbooks seem to be trailing the rest of the books. None of that is stopping the really innovative teachers though. Not in universities, not in community colleges and not even in high schools. Brian Scarbeau has been blogging about his plans for an XNA-based high school computer science course next year. At his post you will find some discussion of scope and sequence as well as information about the resources