Possibly a most archetypal example of Goodhart's law:

"When a measure becomes a target, it ceases to be a good measure"

Parents find kids get ahead by not only good grades but also by winning in science fairs, sports, or disability claims, so they figure out ways to game those systems . . . and, their value as a measure is eliminated.

With few exceptions, these are now only a measure of how well their parents gamed the system.