[happyopossum]

ACT scores trail education outcomes by ~10 years, as students in school in the middle of a shift don’t get the full benefit from it - they’re often not included in policy changes for the sake of continuity (you may not be able to suddenly change the way you teach math in 5th grade).

[gcmeplz]

State-based ACT scores are also highly influenced by who takes the ACT. If more students choose to take the ACT, the scores might go down even it's because your education system is doing a better job because more kids are trying for college.

For the same reason, you'll see some surprising state scores for SAT/ACT. If you're in a state that prioritizes the ACT, the main students taking the SAT are the strongest students who are looking at out-of-state schools.

Aside from the time lag, I don't think you can look at voluntary test scores and draw many useful conclusions from it.

[keenmaster]

The main changes to reading instruction were made around 2013, and math instruction in 2016. I wouldn’t expect a decrease in ACT scores 12 and 9 years later respectively, even when considering that it takes some time for instructors to master the new approach.