L. P. Benezet (1935/1936). The teaching of Arithmetic: The Story of an Experiment. Originally published in Journal of the National Education Association in three parts. Vol. 24, #8, pp 241-244; Vol. 24, #9, p 301-303; & Vol. 25, #1, pp 7-8.
I imagine there’s been some research done on this since then?? Not my area of expertise, but I’m curious.
P.S. You gotta read this anonymous comment that appeared on Gray’s blog. I have no idea if the story is true, but based my recollection of teachers from elementary school, I can definitely believe it!