pros- pretty good schools, the whole ferry experience is great for fostering independence, safe environment, lots of nice kids and parents
cons- can be hard socially if all of the activities are on-island, the ferry can be a pain if the parents need to go to meetings and games and whatnot (not to mention they play games on the peninsula too), getting rides to and from the ferry on the Vashon side is a hassle for kids if for whatever reason (eg. sports practices) they can’t get the school bus
bottom line: The ferry is a double-edged sword. Schools are good but went a bit downhill over the years in our experience and I’m not sure they’re that much better than the local schools, which seem to be improving a lot. It can be a great experience for some but it’s not for everyone.