Also each of the public school districts ahve their own web sites:
Check out, Seattle, Shoreline, Highline, Northshore, Renton, and Bellevue. Many contain demographis information and things like WASL scores to help you make a comparison.
I used to work in the public schools so if you have specific questions, feel free to contact me.
The Seattle Times School Guide is a really good place to start. Put in the City and click public or private schools.
If you tell me where your children go to school now, and the State you are in, I may be able to point you to comparable schools to what you have now.
I can't specifically say anything about the Seattle School District having never experienced their system first hand. They recently hired a new superintendent to right the ship ...but i'm not sure what was wrong with the ship in the first place.
When I'm researching new areas for clients, ...the site I've referenced is a great resource to see how schools stack up with each other. In the top right corner, there's a link called Compare My School. Click that and you can select 3 schools from any district to compare head to head. It's quite interesting data.
Also, ..one of the district you didn't list that I know is really good is Northshore school district. Edmonds is also good too.