Experts have drafted new national guidelines to help diagnose people with autism.

The research-based guidelines are designed to overcome wide variation in diagnosis methods used between states and territories in Australia.

It is hoped that new assessment criteria will help thousands of people on the autism spectrum connect better with the health, education and disability sectors.

“Each state has been essentially having their own way in which autism is assessed,” said Professor Andrew Whitehouse, one of the expert that developed the new guidelines.

“But even within states, it's not uncommon for children to be diagnosed in early life, but when they meet the school system and the education system require a reappraisal to check if this child has autism.

“I don't know how we've gotten into this state, but it has to change and that's what we're doing today.”

Professor Whitehouse said it would be difficult for some states to change.

“It's going to be a challenge because people have been doing their own thing for a long time, and there is always a challenge in that kind of inertia,” he said.

“What we're looking at here is providing consistency in a diagnosis, and beyond that you get appraised for functional support needs, which is where the NDIS comes in.

“It's been a really important aspect of this guideline that there is flexibility in, so the process can be tailored to the individual who is in front of us.”

Autism educator Bernadette Beasley said they could help girls and women in particular.

“Girls in general do show a very different profile to boys, and I do believe that's one of the components where they're late in diagnosis,” Ms Beasley told the ABC.

“The girls we work with now, we're picking them up around 10 or 11 with anxiety, depression, self-harm, and we believe this tool will get these girls much earlier.

“What's happening now is in school is they hide, they mask their behaviour and people are not picking it up.”

Ms Beasley said reaching an appropriate diagnosis early helped avoid later stress and pain.

“They go home and explode with anxiety and sensory overload, and their parents are saying; ‘We know they're on the spectrum but nobody's listening to them’,” she said.

“They're just being judged as poor parents. We know this is going to make a big difference for women on the spectrum in the future.”

The guidelines have been sent out for consultation.