I always remember when I did some autism training years ago and given this advice.
You either have autism or you don't. It is like being pregnant, you may feel sick in morning, your periods may even stop but it doesn't mean you are pregnant. Some people, like my grandson, have traits of autism but he does not have autism.
At pre-school his parents were told he seemed a 'little' autistic. I agreed that he did have traits but my son was adamant the pre-school were wrong. They then had a nightmare few months ending in a visit to a specialist who said no, he wasn't autistic and the pre-school were wrong.
Fast forward to his now starting secondary school after being very happy and achieving in primary school. The records were still there from pre-school and on a visit to the secondary school he underwent an assessment without my son's knowledge. He was very angry as you can imagine and made a fuss which in the end led to an apology.
It can be a minefield. My son and his wife went through a lot of distress at this time and I learned to keep out of it. In this recent episode I just listened, and did not interfere at all.
I suggest you take a step back too and let things take their course.
No amount of box ticking or labelling will change the fact that he is your grandson and you love him.
Is this behaviour appropriate.
how are schools handling students who memorize books but can't actually decode
