There is one school district in NY which noticed that all the homeschoolers used Saxon math and all their kids did exceptionally well on the standardized testing. They looked into it at the elementary level, Math 54, 65, 76,and 87, and liked it so much that they used it for their elementary schools and THEIR standardized test scores went up.
John Saxon was an algebra teacher who was disappointed in the results he was getting with the standard texts. After studying older texts from earlier in the century he noticed that after introducing new mathematical concepts they would constantly review those concepts before giving the kids new material to master. And that’s how he designed his math program.
It’s common sense. Give the students plenty of chances to review material so they retain their skills.
Public schools continually experiment with new methods without bothering to study the research, if any, to see if it works. This is true of language arts, math, science, etc. Perfect way to dumb down the schools.