I often despair at how perfectly sensible measures are only implemented when situations have become desperate. Chidlren's behaviour is down to both parents and schools. Parents cannot help with behaviour at school if they are not there to witness or control it and vice versa. Both have to work in tandem. Removing virtually all disciplinary measures from schools merely sends a message to trouble-makers that they will get away with unacceptable behaviour.
Equally, parents have to accept that the way children behave in school is not going to improve if they (the parents) refuse to acknowledge that they are in some way accountable for their children's attitudes.
Boundaries have to be set both at home and at school and measures taken if children go beyond those boundaries.
I would point out though that parents can't be expected to help if they are not informed of their children's behaviour. I was astounded to learn, weeks after I'd been forced to withdraw DS1 from primary school because of the school's failure to protect him from persistent bullying, that the perpetrators' parents had at no time been informed of their children's actions.