This trend is known as "redshirting." It's a term coined for college football players who maintain an extra year of sports eligibility by practicing with the team as freshmen but not playing in games.

The idea of redshirting preschoolers has blossomed in the wake of a 2006 University of California at Santa Barbara study.

This doesn't merely mean whether she knows her ABCs but also whether she knows how to get along with her classmates.

Before deciding whether to enroll your child, take notes on her behavior and development.

"The most important thing you can do as a parent is to get to know your kid better," says Anatoly Belilovsky, M.

In it, he uses statistical analysis to prove that a disproportionate number of professional hockey players are born during the months of January, February, and March, lending further support to the theory that kids who are among the oldest in their class have a developmental advantage that boosts the odds that they'll excel in school, on the sports field, and in many other aspects of life.

These influences have helped turn the idea of holding kids back into a national trend, especially among boys (who are generally less mature than girls at age 5) and children born in the latter half of the year.

The same study showed that the oldest middle-school students outperformed younger classmates by 2 to 9 percent, and that high-school students who were among the oldest in their class were nearly 12 percent more likely to enroll in a four-year college or university.

Another factor influencing redshirting has been Malcolm Gladwell's 2008 bestselling book, Outliers: The Story of Success.

(Most states require a child to be 5, or turning 5, by the end of the calendar year when he starts kindergarten.

For parents like Bonawandt, delaying the start of school is a logical way of working around what they feel are unwelcome changes in the elementary- education system.

Researchers Kathy Bedard and Elizabeth Dhuey found that grade-schoolers who are among the oldest in their class have a distinct competitive learning edge over the youngest kids in their grade, scoring 4 to 12 percent higher on standardized math and science tests.