Moreover, in addition to making spaced repetition feasible, it minimizes the amount of review (subject to the condition that you're getting sufficient review) which allows you to make really fast progress.
We (Math Academy) don't have any official academic studies out at the moment, but if you want some kind of more concrete evidence of learning efficiency, you can read more online about our original in-school program in Pasadena where we have 6th graders start in Prealgebra, and then learn the entirety of high school math (Algebra 1, Geometry, Algebra 2, Precalculus) by 8th grade, and then in 8th grade they learn AP Calculus BC and take the AP exam.
The AP scores started off decent while doing manual teaching, but the year we started using our automated system (of which the SRS described here is a component), the AP Calculus BC exam scores rose, with most students passing the exam and most students who passed receiving the maximum score possible (5 out of 5). Four other students took AP Calculus BC on our system that year, unaffiliated with our Pasadena school program, completely independent of a classroom, and all but one of them scored a perfect 5 on the AP exam (the other one received a 4).
Even some seemingly impossible things started happening like some highly motivated 6th graders (who started midway through Prealgebra) completing all of what is typically high school math (Algebra I, Geometry, Algebra II, Precalculus) and starting AP Calculus BC within a single school year. Funny enough, the first time Jason & Sandy (MA founders) saw a 6th grader receiving AP Calculus BC tasks, Jason's reaction was "WTF is happening with the model, why is this kid getting calculus tasks, he placed into Prealgebra last fall, this doesn't make any sense," but I looked into it only to find that it was legit -- this kid completed all of what is typically high school math (Algebra I, Geometry, Algebra II, Precalculus) within a single school year.
Anyway, some links if you're interested:
* https://www.mathacademy.us/press
* https://www.reddit.com/r/homeschool/comments/16hn9f5/comment...
* https://x.com/justinskycak/status/1810482435940913502
* https://x.com/justinskycak/status/1812557234028839193
Again, I realize these are not official academic studies, but we're completely overloaded in startup grind mode right now and have so many fish to fry with the product that we just don't have the time for academic pursuits at the moment, let alone much sleep. Happy to answer any follow-up questions that you might have, though.