Best of luck in your home search.
After looking up the community of Isle of Palms, there are three high schools shown. Two of the HSs I know of but not the other. If there is a particular address, then I could check the HS listed for that address. Of course the school board can always redraw the lines.
I will check on this matter for you and get an answer based on listings within Isle of Palms. It is best to confirm through the school board, since all zoning is subject to change.
My research is showing me that Sandalwood is the High School. Duval County does not have a system online like St Johns County. You must call The Duval County School Board to give them the address and see which one fore sure. The school choice hotline is 904-390-2144. Hopefully this will help you.