Why is Cassie gonna do to the kids on the bus?

Stacey, Little Man, Christopher-John, and Cassie make plans to get back at the bus driver and his passengers. They meet at the school toolshed during lunch and take buckets and shovels, which they then carry back to the spot where they were forced off the road. There, they dig a ditch across the area that fills with gully water and makes it look as if the road washed out from the rain.

After school, they rush back to the spot that they had worked on. As a result of hard rain during the afternoon, their "yard-wide ditch" has become a "twelve foot lake." They hide in the forest bank and watch as the Jefferson Davis schoobus approaches. Thinking that it is a puddle, the driver drives the bus straight into the hole, breaking the axle and waterlogging the engine. The white kids fall in the muddy ditch on their way out of the bus and must walk home in the rain. The bus driver tells them it will probably be two weeks before the bus can be towed and fixed.

they are gonna play a trick on the bus driver