Each school district (and I have been involved in several districts throughout the country) is different, and occasionally even the individual schools have their own tweaks. Two levels to approach it are the HS Counselors - by their reaction you will know if this is something considered run of the mill or completely unique. You may already have the District or State Policy concerning course equivalency (which is what some homeschoolers have to go by) and testing.
On occasion, a high school has chosen to require a student to retake a State Test because their scores were too high before offering up any credit at all.
If my son's experience with schools is any indication, there are many roadblocks along the way to course or State Test equivalencies, especially in the upper grades. I hope somebody else has a better answer for you.
