Best practice in my opinion should include abstract and concrete (real) practice- no one learns everything the same way, so nothing should be taught the one way.

I agree! Some significant research from the early 20th century is confirmed by these findings you report. There were entire schools where the language of math was taught before the algoritms in the earlier years.

For myself, I was VERY lucky to have learned math in the era of the first wave of NEW MATH. The basic core research concept was to teach the use of the variable(abstract) in the place of a blank space and to use algebraic (horizontal) algorithm formatting. I didn't have.

Interesting topic;D Thanks!