A nursery school teacher observed a group of 28 children during a 30-minute play period. She evaluated the aggressiveness of each child on a scale fro

A nursery school teacher observed a group of 28 children during a 30-minute play period. She evaluated the aggressiveness of each child on a scale from 1 to 10 in which 1 meant highly aggressive and 10 meant highly nonaggressive. The children then watched a puppet show designed to elicit cooperation and suppress aggression. After the show, the children were re-evaluated on the scale of aggressiveness. What design would determine if the puppet show was effective?