Yes, the effect is very dramatic over the last 10-20 years, but I suspect it's been hard to document. It's clear in terms of some expectations: a generation ago

Yes, the effect is very dramatic over the last 10-20 years, but I suspect it's been hard to document. It's clear in terms of some expectations: a generation ago, it was expected that children would learn the alphabet in kindergarten, but today children are expected to enter kindergarten knowing the alphabet. So many kindergarten classes spend a few weeks reviewing the alphabet before rushing into words, leaving behind some children that didn't get pre-school before the age of 5. http://www.npr.org/sections/ed/2016/01/08/462279629/why-kindergarten-is-the-new-first-grade http://www.npr.org/sections/ed/2016/01/08/462279629/why-kind... "In 2010, prekindergarten prep was expected. One-third more teachers believed that students should know the alphabet and how to hold a pencil before beginning kindergarten. Everyone should read. In 1998, 31 percent of teachers believed their students should learn to read during the kindergarten year. That figure jumped to 80 percent by 2010." http://blogs.edweek.org/edweek/inside-school-research/2014/01/is_kindergarten_the_new_first.html http://blogs.edweek.org/edweek/inside-school-research/2014/0... ".The percentage of teachers who reported their students never received physical education more than tripled, from 14 percent to 45 percent" https://www.bostonglobe.com/ideas/2015/06/13/common-core-killing-kindergarten/lydG3pnscVEnTEoELUZWdP/story.html https://www.bostonglobe.com/ideas/2015/06/13/common-core-kil... '“When we require specific skills to be learned by every child at the same time, that misses a basic idea in early childhood education,” she says, “which is that there’s a wide range to learning everything in the early years.”' Meanwhile in Scandinavia children don't even begin formal education until they're 7.