you are confusing the diagnosis with other factors that may have affected his behaviour way more than any parent of a child with SEN buster!
my son is, i think, a success story, he does not have adhd, but does have several other disabilities (asd, dyslexia and dyspraxia) He was never angry or disruptive in class, more likely to be the victim than the perpetrator, this did not however, stop certain teachers misunderstanding him or making his life very difficult, or as you are in the case you mention above, blaming his parents.
but despite teachers like you, (im pleased to say the majority were supportive and helpful) he gained excellent GCSE results, wobbled his way through A levels and has done a foundation degree, embarking next year on his third and final year at uni and living away from home for the first time. he is a success. he holds down a job, and is on track to get a first.
i do not believe that withholding his diagnosis would in any way of been beneficial to him. He needed to know WHY he was different, and his dx explained this for him, and was such a relief to him and us. It did NOT give him carte blanche to misbehave, but buster you seem to have stereotyped all pupils with disabilities and their parents, and thats a shame. attitudes like yours really do more harm than good.
im used to it now, and its water off a ducks back.
My sons IQ is way above average. He knew he was different from an early age. he needed to know why, and accept it.
Your attitude really saddens me, but does not surprise me in the least. the absolute worst years of my sons life were his school years, and he openly says the same. perhaps one day hidden disability will be accepted for what it is - a disability, without scorn or scepticism within schools. but it seems that nothing much has changed in 19 years.