He's not "blaming" anything on immigrants; he's saying the simplistic statistic presented is confounded, and is unlikely to show the direct correlation between funding and student outcomes that it purports to show.

You're required to be charitable here; it's in the site guidelines. Yours is not just an uncharitable interpretation, but a deliberately inflammatory one.

No. I am not going to be charitable to an obvious attack on immigrants.

It wasn't "an obvious attack on immigrants", as anyone who's read many of rayiner's HN comments would know. Please follow the site guidelines.

...because the new demographics are significantly generically stupider?

You can put a math prodigy in a room with me and I will have a harder time teaching them (anything) if their Spanish is good and their English is weak, because my English is good and my Spanish nonexistent. "Stupid" has nothing to do with it.

...because they’re being tested in a language their parents often don’t speak at home?

Cause is easier to blame Mexicans and South East Asians than insufficient school funding.