This is the same question as how does one compare the written curriculum to the taught curriculum to the tested curriculum.
First, to compare the written (intended) curriculum to the taught (implemented) curriculum, curriculum mapping is a technique that is very useful. Essentially, a curriculum map is created by the teacher of the subject by recording what s/he is actually doing in the classroom at various points throughout the day. Fenwick English offers a method and background on doing this. This map is then compared to what is actually written in the school district's curriculum guide.
A second analysis is backward mapping. That is, analyzing items on a culminating test (perhaps an achievement test or final exam) to determine the actual achieved curriculum. These test items are then compared to the written curriculum and the mapped taught curriculum to find gaps and overlaps.