Another consideration is the definition of “grade level.” While standardized tests may use this team, it’s pretty clear that grade level varies widely depending on area and specific school, at least in the US. The common core was an attempt to standardize things but it’s clear there are huge variations.

This is illustrated in a nyt article, recently re-posted by aeh on a different thread.

https://www.nytimes.com/interactive...s-how-your-school-district-compares.html