Many educators believe that children are better off in kindergarten -- and more primed for success generally -- if they enroll when they are older than most classmates. This belief in academic "redshirting" (named for the athletics practice of keeping players off the field for a year to extend eligibility) leads to many parental debates on the relative merits of enrolling junior in public school as soon as possible or a bit later. Some parents even attempt to time birth with cutoff dates in the school districts in which they live.
The impact seems especially logical in early education, where eight months of age difference of two kindergarten students can mean (given young ages) that the older student has a substantial edge over the younger students. Some have extended this well beyond kindergarten. Malcolm Gladwell,  for example, has argued that those who start school timed so that they are older than their classmates (and who are hockey players) are more likely to be drafted, and drafted high, by a National Hockey League team.
But what about Ph.D.s? Are you more likely to be one if you were strategically redshirted as a child? If you want your children to follow in your footsteps, should you place your offspring in kindergarten as late as possible?
It turns out that whatever academic benefits redshirting may have early on (or for hockey players) don't show up when it comes to earning a doctorate. The Cornell Higher Education Research Institute has released a paper  by Kevin M. Kniffin and Andrew S. Hanks, two postdoctoral fellows at Cornell University, who analyzed the question of "relative age effects" (as the topic is called) on doctoral education. Controlling for discipline and other factors, they found no impact of the start date of one's elementary education on the age at which one earned a Ph.D. or post-Ph.D. salary.
The scholars identified new Ph.D.s from the Survey of Earned Doctorates, their birth dates, and the cutoff dates for kindergarten enrollment (placing students in the states in which they were born to allow for comparisons across the United States). They could find no benefit (or cost) for doctoral students having started school later.
Kniffin and Hanks acknowledge in the paper that they don't have data for those who started but did not complete a Ph.D. and that they assume similar levels of redshirting from state to state (since they don't know how many parents of Ph.D.s engaged in the practice). But they write that their study shows that by the time students reach doctoral level education, any positive impact of redshirting seems to have disappeared.
At the same time, the authors used the income data (combined with trends on inflation and retirement data) to estimate the average impact of academic redshirting on a Ph.D. recipient's lifetime earnings. Starting a year later will over the course of an average academic career cost someone with a Ph.D. a bit more than $138,000.