Grounded For Life

current mood: stressed
A call from the principal's office is never a good thing. This afternoon, the assistant principal at my son's elementary school called to say that my son and several other boys were sitting in his office, having been caught during recess throwing rocks at cars in the parking lot. These are not disgruntled teenagers. These boys are first-graders, all of seven years old.
A car belonging to a fifth-grade teacher was damaged. She's going to get some estimates for repairing the damage, and each boy's family will have to pay an equal share of it. Unfortunately, the car was a BMW, so I imagine it will not be cheap.
I'm mystified. Why do boys do lamebrained things like this? What were they thinking? My son is not home from school yet, but when he arrives, we will have a talk, and probably not a pleasant one.
If anyone out there has been a seven-year-old boy and understands the motivation behind such an act, I would really like to be enlightened.
You should ask Mike. I remember his boy had at least one incident of mindless destruction while growing up....