Crash Course in Public School Ratings
California is home to many nationally acclaimed public schools, and buyers are willing to invest incredible amounts to secure houses in these areas. Property values in good school districts also translates into better long term stability. Homes with highly rated schools appreciate more quickly in a strong market, and depreciate at a slower rate in recessionary periods.
Two common school rating systems in California include the API (Academic Performance Index) and the Greatschools.org 10-point rating system.

The API (Academic Performance Index)
There can be a lot of variance between school ratings on a 10 point scale because APIs range from 200 - 1,000, and every school aims to score an 800 or above. Scores are based on standardized test scores, including the STAR (standardized testing and reporting) program and CAHSEE (CA HS exit exam), which have been used since 1997. Any school that does not meet the 800 rating goal sets a growth target for the next year.

The last time annual API scores were released was in 2013, and 3-year averages were released in 2014.
2013: Changes to School Ratings
In 2013, California adopted Common Core State Standards and STAR testing was suspended in order to transition to a new and more balanced system. The new assessment system, California Assessment of Student Performance and Progress (CASPP), calls for new academic content standards, assessments, and accountability.
Although no new ratings have been released since 2013, many people continue to use APIs as a reference point. Relying solely on a school's API can be misleading because school performance may have changed since 2013. For example, Rosemary Elementary school in the Campbell Union school district has a 2013 API of 834 and a Great Schools rating of 4/10.
The Great Schools 10-Point Scale
Greatschools.org is a great resource for the most recent information regarding state test scores, parent feedback, and equality demographic data. Ratings are broken down into three categories:

1-3: "below average"
4-7: "average"
8-10: "above average"
In California, the basis for these ratings are the school's average standardized test scores relative to other students in throughout the state. In addition to the 1-10 rating, this data is broken down into Science, Math and English, as a percentage compared to the state average. The ratings are distributed as a bell curve.
Check out the GreatSchools rating of any public school in the US here.
Never assume that a property falls within a certain school district. Zillow, Redfin etc. do not guarantee the assigned schools they publish for each property.
When purchasing a home, always call the school district and confirm the assigned schools for that property
Check both school APIs & Great Schools ranking to evaluate school performance
School rankings change in time, and schools are always striving to improve their test scores and parent satisfaction. An average school today may become above average in time.
Consider the age of your children and timeline when making decisions buying for specific schools. If you have a newborn, you are likely to move before your babe hits high school.
Have questions about Bay Area school ratings? Email me roxy@roxyrealtybayarea.com