They don't grant degrees or diplomas. As such it is presumably accredited as a Supplementary Education Program and (like JHU CTY, Stanford ULO, and AoPS) do not grant credit. Such programs can be the basis of credits if your "real" high school accepts them, though.
Right, ymmv for transfers at either a hs or college. But the accredited status makes it possible to get approval. MA say they can make the documentation available manually and will automatically in the future.