I get the feeling that you are looking for the perfect test score that you will be able to show to your DS's school and have them instantly recognize the needs that you see. I would be tempted to try the opposite approach. Instead of looking for more tests to convince them of your position, why not ask the school what they would need to see. For example, if you think your DS should be placed in 6th grade math, then ask them what they would need to see from your DS in order to put him in that class. If they tell you that it's simply not possible (for whatever reason) then at least you will know their position and can stop putting so much effort into something that will not achieve your goal and can turn your attention to some other strategy for addressing those needs.