As private kindergartens prepare to send out acceptance letters this week, competitive parents are trying to game the system with so called “red shirting”—delaying their kids start in school so they'll be more advanced then their classmates. Kristina Dell on why it's backfiring. Holly Korbey's son, Holden, was easy to spot in his kindergarten class—he was the one who actually looked kindergarten sized. "The other kids were just taller," says his mother.
 That's because unlike his classmates, most of whom were six years old, Holden was only five—the traditional kindergarten age. But entering kindergarten at age six is becoming more...
