The road to understanding autism is unfinished, zigzagging and punctuated by speed bumps, the first of which is the question that transformed my life as a dad in 2008: “What is autism, anyway?” My son was three years old when he was diagnosed, but autism resists definition, vigorously. Google Down’s syndrome or Parkinson’s disease, and you’ll get a broadly agreed-upon set of causes and criteria. Google “autism”, and you get a can of worms, a minefield, academic papers and a shouting match. Despite the prevalence of phrases like “autism epidemic” and suggested “cures”, autism is not a disease (an illness caused by a known biological agent), but a syndrome – a cluster of symptoms, or the disorder associated with them. These symptoms cover a lot of tangled ground: impaired communicative and social skills; scrambled sensory processing; delayed childhood development; poor motor functions; an aversion to eye contact; tendencies towards repetitive behaviours, spinning and rocking motions. Some of these were visible in my son; just as many were not.

Confusing things further were the two best-known portraits of autism in popular culture, in the 1988 film Rain Man and Mark Haddon’s excellent 2003 novel The Curious Incident Of The Dog In The Night-Time, which depict not mainstream autism but Asperger syndrome. Was our son going to turn out like Dustin Hoffman’s savant or Haddon’s teenage mathematician? It looked unlikely. But if not them, who? There was no answer, and attempts to discern my son’s future felt as futile as they felt depressing as they felt impossible.

Don't assume that behind autism's speechlessness lies nothing, or nothing to speak of. Talk to the person

Autism’s symptoms vary widely from person to person, and change over time. There’s an evergreen adage: “If you’ve met one person with autism, you’ve met one person with autism.” Very true, but it was a truth that didn’t help the anguish of those first two years, when the dominant message is: “Hurry! Early intervention is crucial, before his neural pathways are set! Save your child from autism before it’s too late!”

How do you “save your child” from something when you don’t know what that something is? Or when nobody even knows what causes it?

The question I encountered from friends, family and relatives – and our second speed bump – was: “So how autistic is he?” Conditions like deafness or visual impairment can be measured on a scale. Autism laughs at scales. Our son’s diagnosis was conducted via the snazzily named Disco test: Diagnostic Interview for Social and Communication Disorders. Disco is dismal. It involves a mammoth seven hours of parental interviews and a meeting with the child, but doesn’t distinguish between what a child can’t do and what a child won’t do when asked, as far as I could tell. It seemed that a bright examiner capable of engaging a child’s attention would arrive at a different result from a tired, unimaginative examiner – implying that Disco’s truest measurement is the tester’s skill at administering Disco.

“Degrees of severity” labels are, I think, inherently subjective. Which is OK – that’s autism – but what’s not helpful is to pretend otherwise. After all, these labels may mean the difference between a decent life in an assisted-living unit and a life shuttled between borstal, homeless shelter, NHS ward and overcrowded prison cell. Furthermore, the current language of autistic degrees bring me out in a rash. “Mild” and “severe” sound like ratings for pneumonia, spicy food or crime. The common “low-functioning” and “high-functioning” bring to my mind a 1980s home computer, or the liquid metal android from Terminator 2. For personal use, I deploy a system based on my printer’s ink cartridges: yellow is at the Asperger’s end of the spectrum, cyan is in the middle and magenta is the most hardcore. “So how autistic is your son, exactly?” “Well, his sensory processing is pretty cyan these days. Speech-wise, he’s light magenta. A nice canary yellow when it comes to motor control and memory functions, mind you. Thanks for asking.”

Anyway, circa 2010 things were pretty grim in our house. My son still wasn’t talking; his eye contact was fleeting; he didn’t do bedtime; and he was prone to meltdowns, which meant an uncontrollable bout of sobbing while hitting his own head or banging it on the floor. This would occur several times a day, for up to an hour, wherever he happened to be, including the supermarket or toddler group. Sometimes the trigger was visible – being separated from his mum for more than a minute – and sometimes it wasn’t. Our special-needs support person suggested we keep a diary of when the meltdowns occurred, which wasn’t a bad idea per se, but neither was it of any practical help with what we were trying and failing to handle.

Around this time, my wife ordered a book online called The Reason I Jump. It was written by a 13-year-old boy from Chiba prefecture in Japan called Naoki Higashida. Naoki’s autism is designated as severe (I’d say “deep magenta”) and non-verbal, but he can, with intense effort, write via an alphabet grid. This is a Qwerty keyboard drawn on a card with an added Yes, No and Finished. Naoki touches the letters he needs to build up words and, eventually, sentences and paragraphs. The Reason I Jump was written this way. (There are clips of Naoki working on YouTube; sceptics can see for themselves that nobody’s hand is near his as he writes.)

Don't worry if there's no evidence he or she understands. Maybe there is, but you're not recognising it

As my wife read sections of The Reason I Jump aloud at the kitchen table, we recognised many of our son’s traits, and found many of Naoki’s explanations for these behaviours plausible. The book is made up of short Q&A chapters, and some of the questions were ones we badly wanted to ask our son: what’s with the head-banging? Why the tears or laughter with no visible cause? How can we help you more usefully? Naoki’s autism is, of course, Naoki’s own autism, but we found plenty of overlap with our son’s condition, and the book provided answers, corrected misconceptions and filled in blanks. Even chapters that didn’t apply to our son directly helped us by highlighting the gap between the “what you see” and the “what’s inside” of non-verbal autism. They also testified to Naoki’s ability to feel the whole gamut of human emotions and to view situations from other people’s perspectives. Before autism entered my life, I had believed the condition precluded emotional breadth and empathy: The Reason I Jump consolidated my wife’s and my suspicions that, in fact, people with autism feel what everyone else does. They just cannot show they feel it, so neurotypical people have come to think of an autistic mind as locked-in and robot.

Thanks to the book, my wife and I found ourselves modifying our interactions with our son. We engaged with him more, expected more back, and followed Naoki’s advice – even if it was as simple as, “Hang on in there and don’t give up: he’ll get there in his own time.” Our son responded positively. He began using a few words, his understanding bloomed, his self-harming dropped away and he was happier. None of this is very scientific, I agree. I can’t know for sure or prove that these changes wouldn’t have occurred anyway, and, heaven knows, bad days and bad patches still happened, still do, and always will. But The Reason I Jump helped us turn some kind of corner in our lives together.

My wife and I translated Naoki’s book into English, not exactly legally, just so we could hand out A4 copies to the people working with our son. We wanted them to know what the book had taught us about autism, and to act accordingly. Encouraged by their positive reactions, I showed our manuscript to my agent, and my UK and US editors. They thought that Naoki’s writing could find a wider audience; though it’s fair to say that nobody foresaw the English-language edition of The Reason I Jump topping bestseller charts on both sides of the Atlantic, selling well into six figures and being translated into 35 languages. An expanded edition of a more recent book by Naoki, Fall Down 7 Times, Get Up 8, also co-translated by my wife and me, will be published this month, and focuses on autism in young adulthood.

Perhaps it’s just vanity, but I like to think the success of The Reason I Jump has encouraged a readership for other books by non-verbal textual communicators with autism – “texticators”, since I’m in a word-coining mood. Notably, Ido Kedar and Carly Fleischmann in the US, and Tito Mukhopadhyay in India have also written insider accounts of life with autism. The authors concur with Naoki on some points and disagree with him on others – and this diversity enriches the literature of autism.

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The word “autism” was first used as early as 1910, by Swiss psychiatrist Eugen Bleuler, to describe a state in which “thought is divorced both from logic and reality”. Autism as a psychiatric diagnosis, with no basis in biology, hobbled on through the 1920s and 1930s as a form of childhood schizophrenia, occasionally awarded to children whose jailers had no other label for them. In 1943, Austrian-born psychiatrist Leo Kanner nominated autism as a disorder in its own right. Kanner deserves kudos for identifying a syndrome badly in need of recognition, for naming it and for encouraging early support groups. Unfortunately, he went with the flow of mother-blaming in the 1950s and attributed autism to “a genuine lack of maternal warmth”, though he did appear to recant towards the end of his life – unlike the Darth Vader of autism infamy, another Austrian-born American, Bruno Bettelheim. This Chicago-based propagator of the “refrigerator mother” theory of autism published his hugely influential text, The Empty Fortress, in 1967. This contained such pearls as: “The precipitating factor in infantile autism is the parent’s wish that his child should not exist.” The cure was psychoanalysis for the mothers, while the children were allowed to “unshackle” themselves by being put in a room with their peers and allowed to do whatever their ids, egos and superegos told them. You can imagine how that went.

Describing Bettelheim as merely “wrong” is a kindness I don’t think he deserves, yet for years his thinking dominated the public discourse. Mothers bought into this cruel farrago because no strong counter-narrative existed, and because if they had “frozen” their children into autism, submission to the faith promised a thaw. (Bettelheim would not be the last charismatic, media-savvy doctor to attract a fierce and loyal following among autism parents who felt ignored by specialists and frustrated by the lack of answers.) Historical perspective lets us groan at Bettelheim, and feel a righteous disgust at other researchers in the 1960s, who electrocuted their test subjects with cattle prods to deter self-injury, or who dosed children’s hot chocolate with LSD. The more ethical even obtained parental consent.

If the person is there, never discuss them as if they're not, or as if they're only there like the coat stand is there

The closer we get to the present day, however, the trickier it can be to discern solid science from “magical thinking” with scientific trappings. At an event at the Hay festival in June this year, my very first questioner asked me to agree that there may be a link between autism and the MMR vaccine. Now, I regret prevaricating, though if I had replied that no large-scale, peer-reviewed, duplicable research free from conflicts of interest has ever established a link, the session could well have died a noisy, messy death in Conspiracyland. Skin is thin. Being told, as an autism parent, that you’re wrong about autism feels very like being told that your ignorance is compounding your and your child’s misery. Little wonder people lash out.

So what are we still getting wrong about autism, and how do we get it right? My answers form a kind of wishlist. First up, is that we stop assuming a communicative impairment denotes a cognitive one. Let’s be wary of assuming that behind autism’s speechlessness lies nothing, or nothing to speak of. Instead, let’s assume that we’re dealing with a mind as keen as our own, and act accordingly. Talk to the person. Don’t worry if there’s no evidence he or she understands. Maybe there is evidence, but you’re not recognising it as such. If the person is there, never discuss them as if they’re not, or as if they’re only there like the coat stand is there. If they don’t notice this courtesy, no harm is done; but if they do, then someone who is often treated as a part-object, part-human, total nuisance gets to feel like a real, valid, card-carrying member of society.

My second wish is that diagnosis day and its aftermath don’t feel like a cursory death sentence with no hope of appeal. On my son’s diagnosis day, a psychologist gave us a photocopied report about how poorly our son had performed in the Disco, a platitude about him still being the same boy he was the day before; and our time was up. We went home, Googled “autism” and embarked on a two-year stress-fest of searching for a kindergarten that might take him, of searching for a home tutor, of jumping through hoops erected by a bureaucracy that feel designed to make you give up, and of chasing “cures”. (The less said about the water I ordered from Texas that had either ions added or ions taken out – I forget which – the better.)

I know that central government has forced local authorities to cut health services back to the bone, and we’re all supposed to accept this as the natural state of things. I know also that parents whose dreams for their children have just collapsed aren’t the easiest folk to deal with. But intelligent counselling, drawing on guidance from parents who have been there, would go a long way to saving the newly diagnosed from floundering as badly as I did. And, as it happens, cost very little.

The third item on my wishlist is, too predictably, better funding for education and adult care. The status quo obliges sleep-deprived autism parents and sympathetic school principals to be frontline activists, just to obtain statutory minimums. This is inhumane and illogical. Funding a special needs assistant now can create a future taxpayer. Not funding special needs education is a waste of a child’s mind. That could be your child’s mind I’m referring to, or your grandchild’s, or a future Elon Musk’s. Speech and language therapy and occupational therapy can and do make big differences, if they are frequent and regular. What the state grudgingly dispenses at present is infrequent and irregular. Better-off families pay to close the gap, if they can find a good private therapist; but what we now call ordinary hardworking families don’t stand a chance. I’ve met some great therapists working in the creaking UK and Irish state systems, but too often the state system appears to be a legal fig leaf whose main purpose is to deter lawsuits brought against education departments for providing nothing. (As an aside, to any bright young people with curiosity and empathy reading this article and wondering about a career, think about autism therapy. Demand outstrips supply, and Brexit is likely to drain the UK’s talent pool still further.)

Lastly, I ask for more big-scale, better-funded research. Much historic wrong-thinking about autism was debunked by research foundations set up by well-connected American autism parents. Bright young scientists entered the field, attracted by the grants, and a genetic component in autism was spotted. (There’s a 60-90% chance of an identical twin of someone with autism also having the condition; and 20-30% for non-identical twins. RIP, Refrigerator Mum.) More research followed, autism conferences grew in number and size, donations snowballed and finally governments got involved. Answers to the same core questions I had after our son’s diagnosis – What is autism, and can it be made to go away? – remain elusive and debatable, but every decade the questions asked get better and the research more fruitful. Autism is now a multidisciplinary field with career-building roles for biologists, pharmacologists, geneticists, psychiatrists, neurologists and a whole platoon of other -ists.

In his book Far From The Tree, the psychiatrist Andrew Solomon quotes Nobel laureate Eric Kandel: “If we can understand autism, we can understand the brain.” Solomon adds: “That is a generous way of saying we will understand autism only when we understand the brain.” True, yet this is a call to mobilise, not a reason for despondency. To study autism is to study the mind, the brain and the body; their connections and ruptures; the human genome, speech, sentience and alternative permutations of being alive. Autism research benefits not only people like my son, but stroke survivors, those living with dementia and the families who care for them, and countless others in ways not yet known. It’s a bold prize. It’s a huge challenge. Let’s rise to it.

• Fall Down 7 Times, Get Up 8, by Naoki Higashida, translated by David Mitchell and KA Yoshida, is published next week by Sceptre at £14.99. To order a copy for £11.24, go to bookshop.theguardian.com or call 0330 333 6846.