Thanks for your reply, Cristiana!
My son was 6 at the time of the test, 7 now. He is generally a bit anxious (is has sensory issues with his clothes which upset him) so that could be a factor for him.
He was eating gluten at the time of the test, but 4-6 weeks before the test he was not, because we tried him on a gluten free diet for two weeks. During...