(No doubt a hair-pulling America-is-falling-behind lament is better for clicks, since headline writers know what they're doing, but undoing their deeds is part of the job here.)
The phrase “specific classes of people” seems to miss the entire point of the parent comment… according to the linked study, all groups of people improved from 1992 to 2015, not just “specific” groups. This is a classic example of Simpson’s paradox. https://en.wikipedia.org/wiki/Simpson%27s_paradox
Imagine, for a moment, that you start a school that teaches reading and writing. You have 10 ELL students and 90 native students. When you test them in 2015, the ELL students score 50 points on average, and the native students score 100 points on average. The average score for the school is 95.
Now imagine that your school is well-known now, and you hire better teachers (all test scores go up 10 points), and 40 more ELL students join your school. Now you have 50 ELL learners averaging 60 points, and 50 native learners averaging 110, so the average score is 85.
Even though everybody’s test scores went up by 10 points, the average test scores went down by 10 points because the demographics changed.
To be honest, this is horribly unfair. Somehow ELL students are seen as “behind” the native speakers when that’s only when you measure them in English. This propagates the idea that it’s better to be an excellent English speaker than it is to be bilingual but less proficient at English. And it’s unfortunate that ELL students who study, e.g., science may get poor grades at times because even though they understand the concepts and know the terminology, the terminology is from their native language.
I’ve heard of one high school where this was especially bad: they had a perhaps laudable goal of encouraging everyone to take APs and go to college but didn’t have the support that requires so recent immigrants were taking AP English before they were even fluent.
There was a worse analytical trap: this problem was masked for years because the school did well on a ranking which measured the number of students taking AP tests against the number of students who passed at least one test because having native Spanish speakers take AP Spanish got a bunch of high scores even though they bombed every other test because they just weren’t proficient enough yet to understand it. I still wonder how different it’d have been if they’d had funding for something like after school language practice.
This does not reflect the reality of US practice, in which students may be labeled "ELL" even if they prefer to speak English at home and/or with their friends. You graduate from the ELL designation by passing a standardized test, so it's more of a designation for "who's stupid" than for "who has trouble with English". It's not really surprising that a group defined by their inability to score well on standardized tests turns in poor scores on other standardized tests.
ELL is a bucket that has people with learning disabilities mixed with immigrants and children of immigrants. The fact that a 14-year-old Korean kid who just moved to America can’t remember the English word for “photosynthesis” is not a reflection of poor skills in science but poor skills in English. I argue that the intent of a science test is to test knowledge of science, and that giving immigrants poor marks for subjects they are good at is nothing more than a failure of testing. This failure should be known and understood when analyzing test results—no test is perfect, but we should be able to account for known sources of error. Simpson’s paradox is the classic example of what wrong conclusions you can draw when you fail to account for variables which are known to affect the result.
I agree with you as to the Korean immigrant. But ELLs as a class are not "behind native English speakers only when you measure them in English". They are native English speakers themselves, and they are behind the non-ELL class because they are selected for poor performance.
I saw this first hand growing up in San Jose in 1970's 1980's. The Vietnam war ended followed by the Cambodian genocide as a result there was a huge influx of refugees and their kids. You had 8 year old's who had spent the last four years in a refugee camp and speak no English at all. I went to college with a bunch of them. They were smart but always trying to catch up with English and writing.
And this fundamental miss-understanding of the point is why misleading titles are such a pernicious problem.
The contention is that no, Americans are actually getting better at reading, but more low achieving students are now being included in the test. This is dragging down the recorded scores, even though students who would have been included previously are getting better scores now (which is the only really meaningful comparison), and also those previously untested demographics are almost certainly also doing better than they were when they were dropping out of the testing regime.