On the radio program A Prairie Home Companion, host Garrison Keillor starts off each show with the words: “Welcome to Lake Wobegon, where all the women are strong, all the men are good-looking, and all the children are above average.”
The tendency to treat all members of a group as above average, especially with respect to numerical values such as test scores, is now often called the Lake Wobegon effect (Word Spy). It can reflect a human propensity to overestimate one’s achievements and capabilities in relation to others (Wikipedia).