H.C.
VV does have a challenge program, however it does not start until2nd grade. I agree with another post. It is likely that much of the skills your children have learned are rote memorization, not conceptual undertanding that will lead to long term academic success. There has been much research on this topic as it relates to play vs academic preschooling.
We are hoping our son will be entering challenge next year. If not we will also be looking into private schools. I caution you to make sure you examine curriculum. I attended a small private grade school and I was further ahead of their curriculum when I started in third grade. Unfortunately they didn't have any programs for different levels within each grade so their only solution was to advance me two grades, which I didn't want to do.