We don't have any NAEP long-term test results for years between 2012 and 2020, because they were canceled due to budget cuts[1], so we can't use the linked data to determine whether the decline started before or during COVID.
We do have the NAEP main series test results[2]. At a first glance at the math results[3][4], it appears they peaked in 2013, then fluctuated through 2019, then dropped significantly in 2022 and somewhat rebounded in 2024, which really does suggest COVID.
Could we look at average SAT scores by year as a proxy? It's not a great metric because not all students take the SAT but I think there's some correlation.
The change was in fact designed to make the scores jump. The purpose is compressing the top scores to allow universities to be more subjective and still have high averages
We do have the NAEP main series test results[2]. At a first glance at the math results[3][4], it appears they peaked in 2013, then fluctuated through 2019, then dropped significantly in 2022 and somewhat rebounded in 2024, which really does suggest COVID.
[1]https://www.edweek.org/teaching-learning/debate-flares-anew-...
[2]https://www.nationsreportcard.gov/report_archive.aspx
[3]https://www.nationsreportcard.gov/highlights/mathematics/202...
[4]https://www.nationsreportcard.gov/reports/mathematics/2024/g...