The API has been the centerpiece of California’s program to hold schools accountable. It compares how a school’s students as a whole perform relative to other schools in California. An API score is a one-number summary of scores on state-required standardized tests.
The API system is organized into two-year cycles, with a “Base” score for the first year and a “Growth” score for the second year. (The Base and Growth scores can be thought of as “before” and “after” snapshots.) In the early part of the calendar year, each school receives a Base score between 200 and 1000 based on its students’ performance on tests given the prior spring.
Schools are ranked annually based on their Base API scores. The State has set a goal of 800 for all schools. Schools are ranked in two ways, but only with schools of the same type—elementary, middle, and high. First, schools are ranked with all others in the state.
Second, they’re ranked with the 100 most similar schools in terms of challenges, based on student characteristics, teachers’ credentials, whether they operate year-round, and other factors. This second “similar schools” ranking recognizes that students’ test scores are strongly associated with factors such as family income, parent education level, and students’ knowledge of English. As a result, schools with large numbers of students from low-income families, for example, tend to have lower API scores. Partly because of the problems in comparing schools with very different student populations, the state created the similar schools rankings.
For both types of rankings, schools are clustered into 10 groups of roughly equal size known as “deciles,” with the bottom 10% of each school type belonging to Decile 1, the second lowest 10% to Decile 2, and so on.
Taken from EdSource, a independent, impartial information source on California schools