Just found a major plot hole.
Arnold is in that school pretending to be a teacher, and the head of school knows he's a cop and why he's there. There's no way in hell Arnold wouldn't have given the head of school a picture of the bad guy, "This is the guy we're looking for." Because at the end the bad guy shows up pretending to be a new parent so he can scope out the school, and the head of school takes him right to his son.
Kindergarten Cop
Kindergarten Cop
"Be bold, and mighty forces will come to your aid."