How Many Years Behind Are Our Students?

Mick Schulz has been considering the American condition, with respect to education, as a story in the Texas v. California saga, and he posts a reader anecdote that ought to make every Rhode Island parent uncomfortable:

A new neighbor (former migrant worker from northern California who opened a family business, and had to move to Houston for a young daughter's cancer treatments) reports to me that when she enrolled her 10 year old in the neighborhood elementary school, they determined that the child was at least a year behind. This is a school with an English-as-a-second-language program, and despite normal demographics which would put it in the bottom rung of schools, won an exemplary rating from the state.

I think the writer meant to suggest that the California school that the student had previously attended had been the "exemplary" one. Which makes me wonder: How far behind are the students of Rhode Island's "high performing" schools? I've long had the impression that these measurements of performance are artificially inflated and, frankly, don't trust them to provide any useful information for judging our system as a state.