Answer: Now! Almost any prep firm's current course is the best prep we know for the SAT, digital version or extant paper version.
The SAT's content is not greatly changing. Students who want to start their prep early (very admirable) will be prepping for the coachable facets of the 2024 SAT.
They will simultaneously be prepping for the fall 2023 SAT. Should a student see in practice even one section with a "Keeper" score (for most competitive colleges a “Keeper” score is a 700 on either the Math or the EBRW portion) we encourage pouncing on it by testing in November and December. Before the paper version is removed, these students with "Keeper" scores have a college admissions credential that will stay with them for the 2024-25 and even 2025-26 admission season.
To answer in a different manner: a large format change is almost irrelevant compared to even a small content change. The format difference from 2023 to 2024 is significant. Students need sufficient practice on timing, expectations, and digital logistics. For some students, it will come quickly, after three, four, or five timed practice tests; for other students, six to 15 practice tests will be needed. Content does not come quickly. There are many skills to master, and now that the SAT is throwing vocabulary back into play, a lot of vocabulary to absorb.
So, even for that rare student who wants to stay away from all paper testing, studying for the content (some math and a lot of vocabulary) makes sense at ANY time. A student who has more time in that fall than in the winter or spring is better off with SAT study now, even if planning on taking solely the digital SAT.
The larger your command of words, the better. The "words in context" section on the SAT is easier for students who recognize the general meaning of words. We say "general" because the section is not testing nuances; the four multiple-choice answers differ significantly in meaning.
This new "words in context" section is unlike the "word most nearly means" question in Reading Comprehension, which is the section that it is largely replacing. Indeed, this new section is closer to the "Sentence Completions" task on the SAT that was used until 2016, wherein the answer choices greatly differed and having a large vocabulary was the best way to ensure right answers.
Word knowledge most directly helps in assessing the answers, but it indirectly helps as a back-up, where understanding the context, the sentences surrounding the sentence with the blank, is necessary to feeling secure about an answer.
What surprises many students (and parents) is that 90 percent of the SAT's math questions stem from classroom math learned in 9th grade and younger. This includes arithmetic, algebra I, geometry, averages, ratios, and low-level functions. Higher level math, including algebra II, matrices, and basic trigonometry has comprised a mere 10 percent of SAT questions. That 90:10 ratio appears to be staying for the 2024 digital SAT.
Students who have not reached these higher levels of math in school can still get perfect 800 scores on the SAT math. The 10 percent of the test might be new can be easily coached by a solid tutor or SAT prep class. It’s more important to master the way the SAT asks math questions: word problems often use convoluted English, straightforward questions often put two skills into a single question (like algebra and geometry, or algebra and averages), and questions sometimes direct unwary students to solving the wrong item.
Thus, the level of math is less important to master than the kind of math. Some students have well-developed–perhaps innate–test-taking skills. For others, a coach can make a huge difference. School textbooks rarely do; textbooks contain straightforward math and cookie-cutter word problems. The math on the SAT demands more versatility.