"So, what have you got on at school today?" I ask.

"Oh, I don't know. Spanish maybe. And sentence-a-day," he replies, taking a delicate sip of his shake.

"Who are you going to play with?" I continue, gently insistent.

"Oh, Dylan and Rove. Not the girls. They're chatterboxes. Can I play on your phone ... please Mum?" He leans in towards my handbag, his eyes searching for the phone.

"Not just yet ... Tell me, how's your milkshake?"

It is not a scene in which I ever thought I would find myself. Five years ago, I would walk past cafes, longing to be one of those mothers who could sit sipping cappuccinos and catching up with friends while their children happily sat in the pram sucking on a Vegemite sandwich. I hated those mothers.

In fact, had I tried when Darcy* was a toddler, the milkshake would have been all over one of us, my words might as well have been in Spanish and the phone, undoubtedly, smashed. Because Darcy has autism.

As he was our second child, I knew what normal development looked like. At 15 months, I realised something wasn't right.

His brother is fairly bright, so I gave Darcy a few extra months.

But he still wasn't saying "Mum", he didn't respond to his name, and he wouldn't look me in the eye. Ever. For months, I would stand at his cot at night and cry, terrified by how he would cope in a world that seemed like another planet to him. Would he ever even say "Mum"?

Darcy was diagnosed with autism and mild developmental delay at two, and reassessed as having "high-functioning autism consistent with Asperger's syndrome" and a "high-average IQ" at age four.

It was a great turnaround achieved through much hard work (and much money spent on therapy), but it brought its own set of challenges. "High-average", "high-functioning" and "Asperger's" do not mean genius. In fact, as soon as you say Asperger's, people immediately think: gifted, superior, savant.

That's why I always use the term high-functioning autism to describe Darcy: to minimise any unrealistic expectations of him.

"High average IQ" just means at the good end of normal, in the average range. Darcy cannot play Tchaikovsky. He cannot quote Shakespeare. He cannot tie his shoelaces - at least, not to any point at which you could let him walk out the door. He reads Diary of a Wimpy Kid. He thinks knock-knock jokes are funny and, given a choice of playing video games or doing his homework, Minecraft wins every time. And that would be a close description of the capabilities and interests of the vast majority of seven-year-old boys who fall in the average range.

The trouble is, as average as he seems, he is not. He has difficulties, sometimes quite pronounced, in social-communication situations. "High functioning" just means Darcy can function: he can sit in a classroom and do most of his work, eat his lunch at lunchtime, and work, mostly, as all children do. It certainly doesn't make Darcy "higher functioning" than the little girl he sits next to. If you walked into his classroom, you might not pick him out. In the playground, it may be a little more obvious.

Where a child without autism might say, "Hey, don't knock my lunchbox over," Darcy might hit the roof and scream, "How dare you kick my lunchbox!" These kinds of inappropriate responses to the most seemingly innocuous situations are thankfully not common, but still occur.

There are other, subtle differences - he will get fixated on insignificant detail, and get ultra-pedantic about rules. He will interpret instructions literally - when I say, "I'll be five minutes," he will time me to the second.

He misses the unspoken social cues that underpin so much of our interaction as human beings. I worry about him not keeping up in school, and about him being bullied because of how he is.

While other kids were drinking babycinos and running around the park, Darcy had more than two years of applied behaviour analysis (ABA) therapy - 25 hours a week of early intensive behavioural intervention, funded in small part by the federal government's Helping Children with Autism package. It cost the taxpayer $12,000 and us another $30-$40,000. The true amount is much higher - both my husband and I became ABA therapists in order to minimise the cost. We still drive a car that was born last century and recently, on a business trip, I had no idea what to do at the airport to check in, because we have not had a proper holiday since ... forever. Hope remains that the National Disability Insurance Scheme will mean intensive intervention is available to all children with autism. It should be: it changes their behaviour and helps them function in normal environments.

Most high-functioning children with autism are accommodated in the mainstream education system, for two reasons: there are not enough places in specialist schools and, for the most part, their parents want them to be able to copy the behaviours of neurotypical children and fit in to society. For us, there was no decision to make.

But that brings another set of challenges. Do you tell the other parents at school?

Do you reduce your expectations of his academic outcomes? What impact will it have on his older brother's social standing? When he has a mini-meltdown - in Darcy's case, sometimes yelling at someone over something minor going wrong - how do you explain why a seemingly average child is behaving like a two-year-old, even if momentarily? Should you feel relieved he yells rather than hits, as a more severely affected child might sometimes do?

We have not told other parents about Darcy's autism, nor have we hidden it from them. I think his classmates view him as equally bright but a little bit weird. He knows he is "special" because he does get a little extra attention, but thinks that's because he is particularly good at reading. I'm not going to correct him, at least not yet.

One of the problems for parents of kids with high-functioning autism is that it can remain hidden, says Kristen Callow, mother of Juliet, seven. Juliet, who was diagnosed with Asperger's at age three, could read at two. "People don't necessarily see all the issues and challenges," Callow says. For instance, as a toddler with about 500 words in her vocabulary, Juliet could not communicate a simple request such as "I want juice." Juliet has struggled with sensory issues, and would have severe tantrums in her kindergarten class. It might mean that she would cry, and run away and hide.

"When the girl friendships get a bit more exclusive as the girls get older, I think it is going to be hard for her," Callow says. "If the child is getting by, be it socially or academically, it isn't raising big alarm bells. We got a lot of 'She's fine', a lot of dismissal of our concerns."

Callow did choose to tell other families about Juliet's Asperger's diagnosis: "We had aides in the classroom, so I felt compelled to let parents know about Juliet. I sent a note home to all the parents in the class. I just highlighted some ways she was a lot like the other children and the things she finds challenging. I wanted to control the message. I just wanted to identify parents who were receptive and make them more receptive. It was amazing, the amount of goodwill."

Although the diagnosis rates of autism are climbing - in the US, the rate is now one in 88 (no Australian study has been done since it was estimated in 2007 that the diagnosis rate was one in 160) - community awareness has not improved.

Whether a child with high-functioning autism has a gifted-range IQ or a normal one, the challenges are similar. There can be large chunks of a day in which their behaviour is perfectly normal, and moments when it is not.

Growing up brings more difficulties. Writes author Benison O'Reilly in the second edition of The Australian Autism Handbook: "Children with high-functioning autism are more likely to recognise that they are 'different' from their peers and this knowledge, especially when accompanied by social failures and occasional bullying, can lead to anxiety and depression, especially in the teenage years."

Asperger's syndrome as a diagnosis will soon disappear, at least officially. The fifth edition of the psychiatrist's bible, the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, which comes into effect in May, excludes the category. Instead, children will be diagnosed with autism spectrum disorder, or a new disorder: social communication disorder, dependent upon functionality.

There is much controversy around the removal of Asperger's, because people with the disorder prefer to identify themselves without the stigma of the word "autism".

But that is not where the emphasis of the controversy should lie. It is unclear whether funding will be available to children diagnosed with the seemingly less-severe social communication disorder. Australia's foremost authority on Asperger's, associate professor Tony Attwood, said research from Yale University showed that "at worst", 75 per cent of those with a current diagnosis of Asperger's would no longer meet the criteria for autism spectrum disorder.

"What we do know is, whatever label we put on the child, they still need support. A child diagnosed with apparently 'mild autism' may have challenges that are profound to them," Attwood says. "If they are offered little or no support, there potentially could be tragic consequences."

Darcy now would probably receive a social communication disorder diagnosis. In fact, I'm sure of it. He's had his funding, so there is no impact on us. What frightens me is the next little boy whose mother's heart fills with fear when he isn't responding. Will he have the same opportunity to function as Darcy did?

I am confident Darcy will grow up into a taxpayer - he has not grown out of wanting to be a builder, though he has not yet discovered that software engineering exists as a career.

Certainly, it is not uncommon for people with Asperger's to excel in places such as Silicon Valley. Indeed, Thorkil Sonne, a Danish father of a child with autism, believes high-functioning people could even be the best at particular jobs, so he created a company, Specialisterne, that hires out technology consultants and employs people with autism spectrum disorder. His company is growing, and looking at expanding to the UK.

But I don't dare think that far ahead. For now, Darcy needs to keep working on having a normal conversation. And that's what Milkshake Tuesday is all about.

The milkshake is almost finished and it's 10 minutes to the school bell. It's been hard work for Darcy to maintain eye contact and chat for that 15 minutes. It's reward time. "Here's my phone, you can play," I say. "What a lovely chat we have had today."

"I love you, Mummy!" he says.

* Name has been changed.

See Kathryn speak at the All About Women Festival at the Opera House in Sydney this weekend.

dailylife.com.au