Stones and a single stick.
There are 196 kids in a playground. Of them only 9 have stones. Some stones are bigger than others and some have more than the rest. In fact one has a small stick but threatens to throw it at people as if it's a stone, unless they're given a free sandwich at lunchtime.
The other kids have all agreed that they don't want to throw stones at each other. Some want to use the stones to draw on the playground, for peaceful purposes. A few of the kids with stones are worried that the other kids with stones who say they won't throw it, might throw it, especially the weird kid who does what the older religious kid tells them to do.
One kid with a shit load of stones is smarter than he looks, and much bigger too. Some of the kids with stones are scared of him and have banded together to form a group of stone wielders who say they'll throw if the big kid throws first. They also promised to protect the smaller kids without stones from the big kid but when the big kid smacks them, all they do is prevent him from using the tuck shop and no stones are thrown.
There is a student council with some kids having permanent places and the power to veto proposals from the other kids, all because they have stones. Although all the kids with stones categorically deny ever wanting to use stones, they're just scared that if they get rid of their stones another kid may throw their stones at them for no reason, or another kid might get some stones and throw theirs.
In the end, nobody throws stones because they're all swapping sweets with each other and nobody wants to lose out on that. Except for the kid that's being home schooled. He's often seen standing outside the gate staring into the school grounds. Everyone keeps an eye on him and are thankful he doesn't have a stone, but right now they need to keep an eye on the big kid. There's also another big kid who keeps himself to himself and is always lending out money for the tuck shop. One day this money kid may want that money back and use his stones.
One kid with stones used to rule the playground but since he's no longer the bully, he still wants school ground "respect" and must have stones, but demand others do not. He pays attention to the home schooled kid, and with their cousin who has far more stones, they shout abuse at the home schooled kid and demands he go away. He often does but always comes back. The big kid tells them to back off and leave the home schooled kid alone and the money kid doesn't want to get involved.
Then one day the home schooled kid gets a single stone and throws it into the playground. It hits one of the kids with a lot of stones and he starts flinging them everywhere. Before you know it everyone's thrown their stones and all the other kids are caught in the crossfire.
The school is closed and never reopens.