An 11-year-old boy labelled as naughty has spent six years struggling at school because of a failure to diagnose him as autistic, his mother claims.
George Evans from Haverfordwest, Pembrokeshire, was finally assessed last November.
A decision was promised within a month, but the family is still waiting for word more than seven months later.
Their assembly member, Paul Davies, has called for a law to make sure children like George get the help they need.
George's mother Beth is certain her son has autism and says his education has been "affected greatly" by a failure to diagnose him.
She says he went to four primary schools, and missed 18 months of his education before he settled in his current school.
"I wouldn't have had to fight so hard personally to get him into the right school," she said.
"His first school was of the opinion that he was a naughty boy and there was nothing wrong him, and he had a permanent exclusion on his record that followed him.
"So it was just a case of trying local primary schools and not getting anywhere because he was labelled as naughty."
Conservative Preseli Pembrokeshire AM Mr Davies said children and adults in Wales with autism were not getting the same support as people like them in the rest of the UK.
Speaking in the Senedd to mark the introduction of his proposed Autism (Wales) Bill, Mr Davies called on the Welsh Government to be "open minded" and support it.
Tory, Plaid Cymru and UKIP AMs joined Labour backbenchers in June 2017 to vote to allow the plans to proceed, while ministers abstained.
The bill - aimed at putting autism services on a statutory footing - will be scrutinised by the assembly's health and social care committee after the summer recess.
Mr Davies - who is also interim leader of the Conservative group - hopes the bill will become law within a year.
"There is overwhelming support for primary legislation and I sincerely hope the Welsh Government will be open minded and support this Bill," he said.
"Similar laws exist in other parts of the UK - and it's time for the same rights to be extended to people with autism in Wales.
"Such a bill could ensure that there are clear pathways to diagnosis and help staff dealing with people with autism get the training they need, so I hope members from all political parties will back the Bill."
Mr Davies has accused the Welsh Government of being "reluctant" to support his bill, but the Welsh Government has said it already has "legislative and policy levers to support people with autism in Wales".
In March 2017, ministers announced an extra £7m for autism services, making a total of £13m to be spent up to 2021.
Responding in the Senedd on Wednesday, Health Secretary Vaughan Gething said AMs needed to ask themselves "whether this legislation at this time will further improve services and outcomes and experience for people", or risk undermining the steps already being taken.
Beth Evans hoped the prospect of new legislation would help her son.
"I do believe strongly that it should be made law that people with autism do have the right to timely assessments," she said.
"There are so many people that are affected and are currently missing out on the quality of life that they deserve because of a disability, and I think that's extremely unfair.
"I think that having those words in law would make a strong statement to the people of Wales in raising awareness."