About my sons academic level?

Can I get my sons academic level tested independently? I don't wholly trust the schools level he is at. I have had to fight his case all the way thru junior school and he has had a good teacher the last 2 yrs who has been able to extend him but I still feel he has more to give and the school ( which failed it's Ofsted) are not bringing out the best in him. He is currently in Year 5