Why are you surprised about this? It's been the way school systems have behaved since shortly after WWII when allowing kids to roam the streets suddenly became undesirable. Mandatory school attendance laws predate this but were not regularly enforced, especially if the kid was bringing a few bucks into the family's income. Parents who created delinquients were often targeted instead of the kid, on the theory that a PO'd parent had a better chance of changing the kid's behavior than the expense of reform school (which had a miserable reputation for doing anything except punishing).
And, as you so clearly point out, the motivation is not the welfare of the kid, or their education, but the reduction in loss of funding for the system.
Seriously, why is anyone surprised? Oh, yeah! With the recent #Occupy shennanigans, holding anybody personally responsible for their behavior seems strange and outlandish.