Basically CC is a one day a week co-op that is academically strong. You can look at Sonlight as your curricula and at CC as academic enrichment. It is the one day you can get out of the house and CC enhances what your children are learning, gives your kids timeline and historical “hooks” to put their information on when they learn it.
In Foundations [done in the morning] they learn memory facts on different subjects: Bible, history, science, Latin, Math, Grammar and Geography. They memorize time line information and one sentence summaries of various historical events. They also cover art, music and a science experiment along with a weekly presentation in front of their class of peers and a family presentation in front of the whole group once a year. These oral presentations in CC give them practice with something that isn’t easy to replicate at home.
Essentials [afternoon classes] covers grammar in-depth, IEW writing and math games (to help them get the facts down pat). There isn’t any reading or in depth study. It is mostly an academically strong enrichment that compliments Sonlight nicely. You would still do a full core but usually you start each day with about a 15 minute review of their CC memory work for that week. If you do the afternoon Essentials in CC you will not need to use the Sonlight Language Arts as it includes grammar and writing.
All this to say Classical Conversation and Sonlight work well together. If the CC cycle of the year matches your Sonlight core theme, that is great, but it is not necessary. If your child is doing Sonlight American History, for example, and the CC cycle is Ancient History, it can still work. Just look at SL as your curricula and the memory work your child is doing in CC will serve him well when he gets to Ancient history. Even though he may not be currently doing a full study in that time period, he will memorize information that will be reinforced when he studies that time period in more depth in later years.
If you have anything to add to this I would love to get your input as I would like to be able to help people put together the best curriculum for their family...whether it involves using Classical Conversations or any other program.