I think the article is implying but not proving this statement.
They are correctly pointing out that the test is essentially norm-referenced (by design) and that this matters if you're looking for improvement (it will mask that improvement) but it also doesn't imply that they're making the test harder.
If anything - the flat line indicates that they're keeping it norm-referenced and that masks change in both directions.
It could well be that they're actually making the test easier since covid, again - to keep the line flat and norm-referenced (hard to tell since a lot of the article's data stops in 2021).
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Essentially - this test is good for saying "How is this school performing vs its peers". It is not good for showing baseline improvement or decline across all schools.
That distinction is important, but I'm also not sure that it matters that much in terms of funding allocation; I'm not deep in the weeds here, so it's possible Texas is missing on some upside, but generally... my assumption is that the "budget" for education is relatively fixed at both the state and federal level, and the goal is not to award states that improve baseline numbers ever increasing budgets, but rather to force states to allocate the fixed resources to schools that are over-performing compared to their peers.
If that's the goal... a norm referenced test makes a ton of sense.
No, it says the difficulty is adjusted every year. You'd see the same flatness whether the entire population was doing better or if they were doing worse.
An alternative headline might read: "Texas’ annual reading test adjusted its difficulty every year, masking whether students are improving or getting worse"
