The pressure to redshirt is particularly high at private elementary schools in Los Angeles, where September cutoffs help to quietly encourage the practice, said Fiona Whitney, author of "The Whitney Guide," private-school guidebooks. By comparison, many other districts -- including Los Angeles Unified -- have December cutoffs.
Most top-notch schools are "very interested in having kids that will fit in," said Whitney, who also counsels parents on education matters and is a proponent of redshirting.
While children of both genders are held back, boys are more likely to start kindergarten a year late than girls, studies show.
"They tend to be impulsive or cry when things don't work; that can be really wearing," Graue said of boys. "Also there's this phobia that you don't have a teary-eyed boy. You want that kid who is confident and strong, who can lead the whole world."