the answer is: empathy
In psychology, empathy is the ability for us to understand the feelings of others.
From the case above, Pete decided to use "Congratulations! Your child is valedictorian!" in his earlier message. This sounded like empty praise that commonly used by people before they ask something to you.
The better method to do this is by appealing to parents' empathy. Pete could begin by telling the parents how highly the people of the school think about their children to make the parents feel pride that currently felt by the school toward their children.