When dd was doing some of the dictation from Bigger, she always got it all right. Then there's ds, who will be in 3rd grade. He seems to remember how to spell words pretty easily. What levels of dictation would I start them in? Does the Preparing guide include the same level that is found in Bigger? If so, I'm thinking I should go ahead and buy the Preparing guide.
I'm having trouble with the idea of letting go of R&S Spelling, so if anyone wants to try to persuade me, go ahead! But I figured dictation only adds a few minutes to our day, so it's not a big deal to do both for a while, right? (Though if we end up dropping the Spelling it'd be nice to do so before they write in the books so I can sell them!)
Anyway, thanks for info you can give me on dictation placement.
As a former Spelling Power and R & S Spelling user, it was tough for me to let go of the "lists", but I decided to give it a year of just doing dictation to see what happened. 3 years and counting - I have not gone back to the lists. Dictation has improved Wyatt's spelling so much, but it has been gradually over the years of doing it. He now tests far above grade level in this area on standardized testing, which he used to test average or below. You have to know, but I'd encourage you to give dictation a try solo rather than doubling up unnecessarily - I think you'd be surprised at the fruit. 
For example, I'd say as they were beginning to write, "Hmmmm, I think you've forgotten something at the beginning" (which they knew meant they'd forgotten to indent). 
I also would give hints, like, "Hmmmm, I think you may want to look at that word again" (which they knew meant they'd misspelled it).