That "myths" link is hilariously terrible. Myth #1 is that some parents use disorders as a fashionable way to cover up poor parenting and bad behavior. If you read the content of the "debunking" as written here on MN, it consists of no joke "these disorders actually exist! Look, here's an organization that says they exist!"
I don't think anyone with half a brain doubts there are children with these disorders. But the idea that it's a "myth" that bad parents sometimes use disorders as a way of excusing inexcusable parenting? That's horrifyingly wrong.
Would you like to know how I know? Oh, I knew you would. Let's have storytime.
My sister and I were often very well behaved in public, but then sometimes quite terribly behaved. We would have physical fights in public. In school, I displayed highly age-inappropriate behaviors like hiding under desks at 13, never handing in homework, being defiant toward teachers even at age 6-7.
At age 10, my mother went doctor-shopping for an ADHD diagnosis. It took three psychiatrists, but she finally found one who'd do it. Got put on meds (which I spat out as soon as I was out of view, because they made me grind my teeth) and everything. My teachers were told about my disorder, and had to make accommodations.
Would you like to know what was actually going on behind those closed doors? It was non-stop, unending physical, emotional, and verbal abuse. My mother hit us with belts, dragged us down the stairs by our hair for talking back even slightly, forced us to do chore quotas that kept us awake all night (gee, I wonder why I slept through classes or seemed distracted), threatened suicide and disappeared for days, called us every sexually degrading name in the book before either of us had a first kiss, and generally made our lives relentless misery.
The signs of severe abuse were there: the tiredness, the defiance, the hitting, the memory loss. But because my mother had done a fine job pasting over the rough bits of our personalities with "behavioral disorders," she was lauded as a fine parent doing a difficult job with kids who must make her life hell.
Surely I'm the only one, right? Nope. Two of my best friends were also put in similar situations -- abused terribly, one sexually, then diagnosed with behavioral disorders instead of anyone getting a clue about what was going on at home.
I'm sorry, but when I see children who develop hitting behaviors that go uncorrected by a parent, I assume they are witnessing extensive corporal punishment and/or outright abuse in the home.
Surely that's a horrible assumption, right? Consider this: according to the NSPCC, 1 in 5 children is subjected to "severe maltreatment" (webcache.googleusercontent.com/search?q=cache:Lg_ptuBrIE8J:www.nspcc.org.uk/services-and-resources/research-and-resources/pre-2013/child-abuse-and-neglect-in-the-uk-today/+&cd=4&hl=en&ct=clnk&gl=us&client=safari). That's 20%. Compare that to ADHD, the most common behavioral disorder, with a prevalence of just 3-5%. Even if you add up all of the behavioral disorders, it's significantly more likely that a random child you see hitting someone is an abuse victim than that they have SN/SEN -- especially if they're not "visibly" disabled, because those with generally-invisible SN/SEN are even less common. For that matter, if even one in ten abusers choose to attempt to disguise their abuse or neglect with a diagnosis of a behavioral disorder (or one in ten abused children is diagnosed with one instead of the therapist noticing the abuse signs), a huge proportion of existing children with SN are also abuse victims.
I know, I know, we're all so special here, we'd NEVER be friends with abusers. My mom's friends thought so, too. They thought she was a lovely woman and we must be such terrible children, while all the time we were hiding bruises under long sleeves.