I spent 2nd and 3rd grade in a grade 1-6 environment (public school). Every student got the same series of math tests and instruction began at the level they fa

I spent 2nd and 3rd grade in a grade 1-6 environment (public school). Every student got the same series of math tests and instruction began at the level they failed a test. Kids could retest whenever they wanted. Older kids were assigned younger kids to broadly mentor. This was the early 1970s. It was by every measure a success. I haven't seen it's like since.