(Guest Post by Matthew Ladner)
“Redshirting” children (having children start school at an older age) has become a fad. Some parents have held children back from entering kindergarten with the idea that their child will benefit academically from being older and/or more mature. According to research by Sandra E. Black, Paul Devereux and Kjell G. Salvanes at Vox (an interesting hybrid between a blog and an academic journal for economists) this fad is like many previous education fads: intuitively plausible but actually worthless.
The researchers were able to isolate the impact of late school starting from those of mere age by comparing Norwegian military IQ tests of students born on December 31 to those born on January 1st :
The administrative rule in Norway is that children must start school the year they turn seven. Children born on 31 December start school a year earlier than those born on 1 January – even though they are almost exactly the same age. This provides an exogenous separation between age and school-starting age.
Result: age matters but not school-starting age. Would-be redshirt parents can relax, or more likely, seek an edge some other way.
Jay P. Greene's Blog 
Eek.
As a first grade teacher I’ll invoke personal experience to say that the majority of the time the kids who struggle are the ones with summer birthdays, i.e. they turned 6 only a few weeks before coming to school for a full day for the first time. I don’t know if keeping them home for an extra year helps, but it certainly doesn’t hurt.
I’ll also offer up that the brightest student I’ve ever had was a September 5th birthday who skipped kindergarten, so it’s certainly dependent on the child and their background.
I agree with the other comment that there may be no research but the students who struggle the most in Kindergarten and 1st grade are almost always our youngest students. I would continue to encourage parents who have young, developmentally delayed, or struggle socially children to give them the gift of time. Plus, I think there is a benefit on the other end. I would much rather send an 18 or 19 year old student out into the real world/college than a 17 year old.
So do you gentlemen find fault with the study, or rather trust your own instincts over that of empirical research?
Don’t get me wrong, empirical research can be wrong and/or incomplete, but the one of the main benefits of doing it is to let us know when instinct has led us astray, as it may have with this red-shirt trend.
[…] Of course, late starters may be less mature and early starters may be especially bright. However, another study looks at Norwegians, who are required to start school in the year they turn seven. Older starters — those with early-in-the-year birthdays — had no advantage over the younger starters with late birthdays. Matthew Ladner writes: “This fad is like many previous education fads: intuitively plausible but actually worthless.” […]