I think you have a great plan to have your 9 year old do the right side of Bigger. He could easily do the science from Bigger to keep it at a better level for him. If he is hanging well with the history portion of Preparing, then I would just keep him there with your 11 year old to keep things easier for you. It is well worth trying to combine for the left side of the plans when possible.
You could easily just keep going with the Storytime set for Preparing, instead of adding in the storytime read-alouds for Bigger too. Your 9 year old will be doing the emerging reader set for his reading so that will be covered. If you already have DITHR, you may wish to consider starting it later this year if you get a chance with just your 11 year old. That would help you get your pace with that program before adding in your 9 year old the following year.
The following year you may very well be able to keep your 9 and 11 year old together for the left side of the plans as they move into the ancients. You may have to read aloud a little more of the core readings than we intend, but we will still be keeping the readings short CM-style, so that shouldn't be overwhelming. Then, your 9 year old would do the right side of Preparing along with the ancients, including the science.
Kiddos grow and change so much in a year's time that you may be surprised at your 9 year olds progress. So for now, just tweak as you've planned, get a good schedule going, and enjoy the journey. You've almost got the placement right now, and I can glimpse the satisfaction that will bring! Make sure you send back anything you are not using, as we'll gladly give you a credit to offset your needed tweaking!
Blessings,
Carrie
