A great resource is http://www.greatschools.net.
They provide information regarding school statstics/test scores as well as other information regarding demographics, etc. In addition there is an option for parents who have children who attend the school to also post comments about the school. This site provides information regarding schools not only in California but in a few other states as well.
If you are looking at schools in the San Francisco Bay Area, you can also check out different school district websites to locate more inforpmation. If you are looking for a particular school district, I can point you in the right direction.
In addition, if you are considering the San Francisco East Bay and surrounding communities, another resource is the Berkeley Parents Network. There is a variety of information regarding schools in the area. Some of the information on the website is not always completely up to date, but if you sign up on the network you can acutally pose you questions regarding schools to parents in the area. The website is http://parents.berkeley.edu/
I hope this helps!
Alain Pinel Realtors