This page provides instructions for getting to the Saxon Research because the Saxon website rejects direct links to specific pages on their website. After a few hours, the link goes obsolete.
Therefore, follow these instructions.
Click on the link below.
Click on "Products" at the top of the page.
Click on "Research" in the side bar.
When the Research box appears, change "Efficacy" to say "Foundational" then Choose Saxon Math for the Category then Click the Search Button. There are 4 article titles -- for some reason they list each title multiple times under different grades. The articles are all the same, regardless of the grade!