Actually having an older brother one grade up may be your biggest hurdle with the Iowa Acceleration Scale. The IAS is just a tool to help with decision making so its not a "test" or a required next step. There has been recent discussion about that on this board.
The fact that ds's school is gung ho is very positive. (My dd is also an acceleration guinea pig. Other than being told to surf the internet at home to complete a research project about beavers it has turned out okay.)
I would figure out some of the logistical stuff like: where is the middle school? where is the high school? are they on the same calendar? maybe ds was to start his day at one school and end his at the other. If so, looking at the course catalogs, can you lump together possible classes. Since they haven't done this before, the out of the box thinking might be there biggest hurdle. For us, a daily schedule that works and doesn't require dd to be in two places at once is just as important as a perfect match academically.
