It's true that in the past, conditions such as autism went undiagnosed, and children with obvious behavioural issues were catered for in special schools. I'm not denying that autism exists and is diagnosed more frequently nowadays, but I do think there is a tendency towards labelling perfectly normal, but naughty, children as soon as they start being difficult.
Also true that many teachers ruled by fear in the past, but it did ensure peaceful classes and a lack of the low level disruption that seems to be the norm today.
My concern is that children today cannot just be 'naughty.' I dislike the namby pamby 'naughty step' and 'gentle hands darling' approach to behaviour that used to be effectively dealt with by smacking.
I was smacked as a child and I smacked my own children when they were naughty. They are now successful women in their forties, and neither of them has ever mentioned being smacked when they were young. They've probably forgotten.
Today, it seems that children have to be diagnosed with a problem when they are persistently naughty. The one that irritates me most is PDO (persistent demand avoidance). In other words, sheer naughtiness and refusal to obey instructions. It didn't exist when I was growing up.