Pew Research Center says that over this period, 2000 to 2024, 78% (2000) to 68% (2024) of Hispanics spoke Spanish at home. To me, that sounds more than sufficient to explain a 20pt NAEP 8th-grade reading gap.
https://www.pewresearch.org/short-reads/2025/05/01/key-facts...
More data is needed here.
FWIW, until 2024, the US treated the state of being Hispanic differently from race, which seems like it could be a confounding factor. (Not that I believe that it explains any of the educational outcome data, but it’s still bizarre and IMO messy.) Here’s the updated guidance:
https://www.federalregister.gov/documents/2024/03/29/2024-06...
If you want more data on something or other, you should state the hypothesis that you are trying to test. Mine is pretty simple and was easy to test like I did in the first post: in a world of mostly static in-group NAEP 8th-grade reading scores (like the one we live in) large shifts in population shares (like we see) dominate the overall average.