American students are regressing in math, and Common Core is to blame, says a scholar from the centrist Brookings Institution.

States whose students took Common Core tests in the 2014 to 2015 school year scored worse on the Nation's Report Card in data released Wednesday, according to Brookings Senior Fellow Russ Whitehurst. "The correlation between Common Core assessment participation and changes in [National Assessment of Educational Progress] is -.35," Whitehurst writes. The differences are statistically significant.

Declines still occurred in states that didn't take the Common Core tests, so the educational standards aren't fully to blame. "This analysis is not causal, and the modest correlation suggests that more is going on than disruptions in instruction associated with the rollout of a new assessment system," Whitehurst writes.

Whitehurst examines only eighth grade math scores, but scores on the Nation's Report Card also declined in eighth grade reading and fourth grade math. National, state, and local data released Wednesday encompassed only eighth and fourth grade math and reading.

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