The age of five is a time you can get your child registered for school, depending on their date of birth.
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But now, many parents prefer to wait an extra year to enroll their kids.
Singing, social skills and study habits make up the 3 S's of Kindergarten.
But some parents delay enrollment for a year so their kids will be among the oldest in class. They see it as the gift of time. The practice is called "academic red-shirting."
But for some parents, time is money.
"If I were to red-shirt my child then I've got another year of pre-school costs and daycare costs," says Jessica Hoff Berzac.
Berzac and her husband have three sons. Walter starts kindergarten this fall when he turns five. He'll probably be the youngest and smallest one in class.
"He's resilient. He'll do fine," she says.
To register in many districts, kids must turn five on or before September 1.
But clinical psychologist Dr. Susan Napolitano says more and more parents are holding kids back, especially if they feel their child isn't ready emotionally.
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"So a kid who's younger and maybe not super advanced socially might have an advantage if you can make them an older kid in the school so they don't become a social outcast," Napolitano says.
Berzac is not a fan.
"I immediately associated it with the concept of helicopter parents and these parents that want to kind of manufacture their children's lives," she says.
The National Center of Education Statistics says in 2010, 9% of the kids started kindergarten when they were already six years old.
"We haven't seen a large trend in our district with that but I heard of that in some of our neighboring districts," says Wendy Hernandez of Central Unified.
Hernandez says another option, transitional kindergarten, allows younger kids with summer birthdays a chance to essentially take two years of kindergarten to improve academically.
"You have to think beyond just right now but think long-term. What would be best for them?" Hernandez says.
In any kindergarten class you'll have younger and older students. But a new study by Harvard Medical School certainly gives parents something to think about.
Tim Layton is a professor of Health Care Policy at Harvard Medical. From a sample of over 400,000 kindergarten students, he discovered a trend.
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"Children born in August are much more likely, about 30% more likely to be diagnosed with and treated for ADHD than children born in September," he says.
The learning cycle is well underway for 5-year-old Carsten. His parents placed him in transitional kindergarten in September but Carsten wasn't quite ready. He kept acting up in class.
"We put him back in pre-school, back into his old pre-school and we've seen a 180-degree turn in his behavior from what it was in the TK classroom," says Alisha Gallon, one Fresno mother.
Carsten is a bright kid who has been diagnosed with ADHD.
"But there are children that grow out of it and I hope he's going to be one of them," she says.
Dr. Napolitano says six months can make a big difference in kids at this age.
"Expecting a child of a young age, especially a boy, to sit still for long periods of time may be more than they can handle."
Most parents wouldn't think of delaying the start of kindergarten. Others though seek not just a social and academic edge for their kids but success in sports as well.
"You want to give your kid every advantage you can," Napolitano says.