Are you planning on pairing with Using Language Well or just using SW alone?
To help with placement look through the samples with “how to use” in mind
https://simplycharlottemason.com/product-links-tips-info/how-to-use-spelling-wisdom/
You want your students to be able to only have a few words per passage that require studying.
The bottom of this page also gives suggested placement, as well as the helpful video that would be helpful in thinking about placement.
https://simplycharlottemason.com/store/spelling-wisdom/
We have really enjoyed using SW and ULW together. Last year my 3rd grader started book 1 (and will finish in 4th grade) and my 5th grader started book 2 (and will finish this coming year in 6th grade). They are not a “race to completion” books though 🙂 Take a look at the samples and see where you think your students would best fit. Growing up I was NOT a natural spelling, unlike my siblings, and I am glad my mom took that into account and worked at my pace.