I absolutely think that you need to ask these questions of the district office right away, before the assessments begin and before you say something to your DS.
Your DS has proven that he is more ready for advancement than most of the other kids in the class, by three separate measures. He should not be assessed again in a fourth manner, unless all the other students are also being assessed at the same time.
You are absolutely right to be alarmed about this and look into it further.
And I would use the grade inflation line of HowlerKarma's if you can fit it in!
