> The writing has to be about a topic for which the evaluator and the writer have a common level of understanding. This means that post-modern literary analysis is useless for teaching writing.

In practice, you're simply criticized for not discussing the context and structure through which you view the work. Arguably that's what critical theory is as opposed to other frameworks of criticism, namely structural theories like marxist and many tracks of feminist thought. Not only is this not a problem at all in practice, it isn't really relevant to the topic at hand because "postmodern literary analysis" doesn't generally exist at the high school and survey level.