In other words, redshirting isn't free or painless to the family or to the adult the student will become.
From the journal: Educational Evaluation and Policy Analysis.
Does the Age that Children Start Kindergarten Matter? Evidence of Long-Term Educational and Social Outcomes (Lincove, Jane Arnold; Painter, Gary. "Educational Evaluation and Policy Analysis", v28 n2 p153-179, Sum 2006.)
Parental preferences and school policies increasingly favor waiting an extra year for kindergarten – particularly for students with summer birthdates who would enter school as the youngest kindergarteners (Crosser 1998; Katz 2000; Stipek 2002). School entry is delayed in the hopes of improving academic or athletic opportunities for children (Katz 2000), but if Angrist & Krueger are correct, waiting an extra year may make students more likely to drop out of school thus reducing life time earnings.
[...] The results suggest that younger students are more likely to repeat a grade, which does have negative academic consequences. However, controlling for grade retention and interactions, starting school young does have modest advantages in terms of lifetime accumulation of human capital. The practice of delaying kindergarten does not appear to create any long-term advantages for students.
This seems to describe our kids school:
There is some evidence that redshirting is an unofficial policy for some school districts, where parents of incoming kindergarteners are pressured to wait an extra year to enroll children with summer birthdates (Shepard & Smith 1986). Other school districts have made the policy official by moving the cut-off date for kindergarten to exclude 5 year-olds with summer birthdates from kindergarten classes (Stipek 2002).
This from the article's conclusions:
Despite past evidence that older students have an academic advantage in elementary school, our results suggest that in the long-run, there is no reason to expect delayed kindergarten entry to increase educational attainment in the long-run. Combined with the work of Angrist and Krueger (1991), this suggests that the most important effect of age at school entry may be that older students lose a year of participation in the workforce rather than that younger students are disadvantaged in early elementary years.
There is no cost to the school for the added years, but the added year of private school tuition for my nephew really does count. And the extra year he will need to be supported by my sister before he becomes a working adult counts too.
Considering all these studies have shown no benefit from redshirting and many real harms to the academic and social development of the kids, and considering the added monetary costs to the families, and considering that many state departments of education as well as several associations of child development experts have come out against the practice, it is a wonder that it is still happening.
The more I read about this, the more upset I am on behalf of my nephew.