I am sorry, but you must be talking to some seriously misinformed people. A child with autism will become an adult with autism.
While it is true that with the right support and education, a child will develop and change and learn coping strategies, they will not "grow out" of autism; it is an integral part of who they are.
When my son with autism was 3, he had virtually no language, no social skills, exhibited bizarre behaviour and regularly had meltdowns.
When he went to school at 5, he still had poor language skills, no social skills and had no idea how to behave. He regularly lay down in assembly, refused to co operate in class and used to hit the staff and other children.
He was not diagnosed with autism until he was nearly 8. By this time the hitting and lying down in assembly had stopped, and he was conforming more at school, but we noticed his behaviour at home was much worse . It was as though he was only just managing to hold it together for the time he was at school and then all hell let loose when he got home. It didn't help that at that time his regular teacher was seriously ill, so the class was having one supply teacher after another - as you probably already know children with autism need routine and stability and to know what's going to happen in advance.
By the time he was 11, our son bore no resemblance to the little boy he had been when he first started school, although he still struggled with language, was emotionally immature and still needed a lot of support at school.
He went to a fabulous secondary school where they put in virtually 1:1 support and he settled really well in a very short space of time. Although he still found things difficult at school he did really well and all the behaviour problems we had up to then stopped. I believe this was because he was given the right support at school by people who understood autism and were experienced in this field.
As the years have gone by, we have met many challenges, but our son has continued to develop in his own pace. Mainstream FE was a disaster as the staff had no clue about autism and just expected our him to fit in with everyone else. Not surprisingly the placement fell down and our son was diagnosed with an anxiety disorder 2 years ago.
He is now 22 and in a specialist college for students with autism. He is making fantastic progress, doing things I would never have thought would have been possible a few years ago. He has learnt to cook, he travels home on the train by himself, and is doing work experience dealing with the public.
I suppose someone from the outside looking in who knew our son as a child might think he has "grown out" of autism, but all that's happened is that it has become less obvious as a result of the education, training and support he has had.
But he still struggles to understand complex language, still has difficulties in social situations and will probably never live fully independently.