I have definitely seen an increase in challenging behaviour over the last ten years. The biggest difference is those increasing number of parents who do not support the school rules.
Uniform, hairstyles, jewellery, lunchboxes - these are small daily breaches of the rules. We see threads time and again on mn about parents bemoaning the 'lunchbox police', etc.
Then there are those parents who don't want to hear that their child has been rude to staff, or unkind to other children and try to excuse it by saying - he's only 5, 6, 7 < insert age >
More serious are those children who cause consistent, low level disruption by being noisy and/or messing about in class. More and more teaching time is given over to behaviour management.
In the past, if the teacher had to speak with a parent, the child would be worried about what their mum would say. Now, so often, parents just say, well school have dealt with it, instead of reinforcing at home.
Parents are more than happy to praise and reward their children when they receive good news from school but when it's a complaint from the teacher, many parents turn their backs on the school and refuse to address or, sometimes, even acknowledge it. That's the biggest change I've seen in schools.
It's a shame because, ultimately, it's the children themselves that are held back. They become unhappy when things don't go their way, they fall out with their friends and are not very resilient to knock backs. They are not very well prepared for real life.
Like I said, the school only have them for a few years but they have to live with themselves their whole life.