From Ed Week:
The youngest kindergarteners in any class are about five times more
likely to be retained in school compared to their older peers, a new
Moreover, educators don't tend to modify their teaching to include a variety of age groups present in kindergartens—but they should make such accommodations, wrote Francis L. Huang, assistant professor in the University of Missouri College of Education, in her study "Further Understanding Factors Associated with Grade Retention: Birthday Effects and Socioemotional Skills," published in the January 2014 issue of the Journal of Applied Developmental Psychology.
The age difference between the oldest children and their youngest peers in any kindergarten might be 12 months—a difference of 20 percent less life experience, Huang wrote.
Their Early Years section had an article last year about holding back a younger-than-the rest kindergartner. This study says that children from wealthier families hold back their younger kindergartener more often than other families, boys are twice as likely as girls to be held back and white children are held back more than black children.
"Delaying kindergarten means finding and paying for another year of
child care," Bassok said. "For most low-income families, redshirting is
far too expensive."
My husband and I held back our younger son (he just missed the SPS cut-off date in September). We could have appealed (and likely got him in) but our thought was that him being one of the youngest AND likely one of the shortest kids, throughout his school years, was not good. It worked for us but we were able to do so and that may not be a choice for many.
This is an important consideration as Common Core comes. I will write a separate thread on this issue but many child psychologists and elementary teachers are speaking out and saying that Common Core is developmentally inappropriate for K-2. Also to note, Governor Cuomo's Common Core review panel said NO kids, pre-K to grade 2 should be taking any standardized "bubble" test.
To protect young children from anxiety and to promote research-based
educational practices, the State should prohibit the use of standardized
“bubble tests” for children in pre-kindergarten through second grade.
This is well-known YouTube video by Dr. Megan Koschnick speaking on this subject of Common Core and younger children.