"When I got the letter telling me about the wait time I just burst into tears," Tanya Wheat said.
"It is absolutely disgraceful, we can't wait two years, my son needs support now."
Tanya Wheat has been told she will need to wait at least two years to get an autism assessment done for her son. (Supplied)
Wheat said she was forced to quit her job as a nanny last year after her son Christopher began refusing to go to school on some days - a move that has put an enormous strain on the family's finances.
Christopher's school principal recommended she seek an autism assessment for her son after noticing he was displaying behaviours consistent with autism.
"He's got all the symptoms of autism. He has some sensory issues," Wheat said.
"He gets worked up and angry and he just doesn't know how to calm down."
While Christopher was clearly struggling at school, he was unable to get any extra assistance without an official diagnosis, Wheat said.
"We've got no funding this year for school, nothing whatsoever, and that worries me.
"We're being left behind and falling through the cracks in the health system."
Christopher was initially diagnosed with Attention Deficit Hyperactivity Disorder (ADHD) while in kindergarten and has been taking medication for the condition.
However, Wheat said her son's behaviour had started to go downhill in recent years and inappropriate behaviour led to him being suspended from school for a period of time last year.
The letter Tanya Wheat was sent, outlining a wait of more than 24 months to get an autism assessment for her son. (Supplied)
Christopher's paediatrician gave the family a referral for an autism assessment at the Perth Children's Hospital through the Child and Adolescent Health Service.
However, in a letter in December, Wheat was informed "the approximate waiting time is currently greater than 24 months".
The letter advised her they would be in touch when an appointment became available.
Wheat said she had no choice but to wait for help in the public health system because they could not afford to get her son's assessment done privately.
Autism assessments carried out by private specialists can range from $1000-$2000 even after Medicare rebates.
"Being on one wage now, we've got no spare money," Wheat said.
"All we can really afford now is to pay the rent, and maybe a bill here and there."
Child and Adolescent Health Service chief executive Valerie Jovanovic told 9news.com.au in a statement referrals to the department had been trending upwards, particularly over the past five years, leading to increased wait times for services, including autism assessments.
"We understand the frustration and challenges parents currently face in relation to accessing these services and continue to work within our capacity to address increasing wait times," the statement said.
However, Jovanovic said most children referred to the service received a planning appointment within eight weeks of referral with a clinician.
Autism Awareness Australia chief operating officer Elizabeth Sarian said it was common for families to have to wait around 12-18 months to get an autism assessment in the public system - with delays sometimes stretching to two years in regional areas.
"Unless the family can afford to go through the private system, they are really left quite helpless," she said.
"There's obviously a lot of time that is lost in terms of being able to support the child and teaching them skills."
Children under seven could usually get some support from the National Disability Insurance Scheme (NDIS) without a diagnosis, however help was usually only available for older children in exceptional circumstances, Sarian said.
"There is definitely a little bit of a gap there for kids who fall into those later primary years," Sarian said.
"And often now, kids - particularly girls - are getting diagnosed around that age."
Getting an assessment and diagnosis was just the first hurdle families faced, Sarian added, with wait times for therapy and support services increasing exponentially in recent years.
"We have an absolute skills and workforce shortage in Australia at the moment," she said.
"It's not state specific, it's everywhere, particularly when it comes to allied health and psychology, it's very hard to find a good provider who has availability."