Hi J.,
You should check out greatschools.net. You can look at test scores, demographics, and how they compare to other schools in that area etc.
Test scores are important, especially in CA, and many schools place children in classes based on them. You will find their API (academic performance index) on greatschools.net and that tells you how that school is doing based on state standards.
I would also do a school visit and talk to a teacher and or principal and observe a class. Don't be afraid or intimidated to do this, you will find them happy to share info about their school. This also gives you a chance to check out the neighborhood, safeness of the campus, and overall feel of the school
I would ask about these things:
Curriculum, do they follow state standards and are all teachers teaching the same things. You don't want a school where the teachers can do whatever they want and not teach key concepts. This happens more than most people realize.
Class size, smaller the better. Most K-3 are 20 to 1.
Facilities, are things clean, safe, do all kids have textbooks, supplies etc.
Classes, do they offer art, music, PE etc in addition to the basic subjects. Many schools are eliminating them because of budget problems.
Support, do they offer tutoring, resource programs etc to help struggling students
Parent involvement, this can make a huge impact on the success of a school
I hope this isn't too overwhelming! I am a teacher turned stay at home mom and I know how important finding a good school is. Good luck!!
S.