Redshirting (academic)
Redshirting is the practice of postponing entrance into kindergarten of age-eligible children in order to allow extra time for socioemotional, intellectual, or physical growth. This occurs most frequently where children's birthdays are so close to the cut-off dates that they are very likely to be among the youngest in their kindergarten class.
Etymology
Redshirting originated as a term for a similar activity but occurring in college sports rather than kindergarten, where a redshirt (noun) was "a high-school or college athlete kept out of varsity competition for one year to develop skills and extend eligibility" and originated "from the red shirts worn in practice by such athletes". The term is an Americanism from circa 1950-1955.
Incidence of redshirting
The National Center for Education Statistics (NCES) reports that academic redshirting occurs at the rate of about 9% per year among kindergarten-age children. The change has been even larger in first grade: over a period of forty years, the proportion of six-year-olds in first grade went from 96% to 84%. Redshirting has traditionally been more common in affluent communities and for children attending private schools, although some scholars speculate that there may have been a recent increase in certain public school districts. According to NCES, boys are more likely to be redshirted than girls, and children born in the latter half of the year are more likely to be redshirted than those born earlier. The NCES report also shows that white, non-Hispanic children are more than twice as likely as black, non-Hispanic children to have entered Kindergarten later than their birthdays allowed.