CCSA created the Similar Students Measure (SSM), as a key component of our Accountability Framework. The Similar Students Measure (SSM) identifies schools that over- and under-perform compared to schools serving similar students statewide. It functions as a "proxy value-add" measure by comparing each school's performance to a prediction based on how schools with similar demographic characteristics perform. It was created as a way to bridge the gap between California's current annual aggregated API snapshots and its reluctance to employ more sophisticated measures such as individual student progress over time.
Similar Students Measure (SSM) Map
A detailed, interactive map which shows all charter and traditional public schools across California and their results on the Similar Students Measure (SSM), which identifies schools that persistently over- and under-perform a prediction based on student background. You can look at how schools in your area compare on the SSM.
How is the SSM calculated?
The Similar Students Measure (SSM) uses three years of annual Percent Predicted API results to identify patterns of performance for charter schools, with the focus of identifying persistently underperforming schools. It was designed to set a minimal bar of performance that allows for uniformly high expectations (API as the outcome), and takes into account students' background. The SSM is used as one component of the CCSA Minimum Criteria for Renewal, which also takes into account the school's absolute API score and 3-year cumulative API growth. It does not aim to replace or supersede the CDE standards of all schools reaching at least an 800 API or all schools reaching their annual growth targets.
For each of the prior three years, schools are categorized by whether their API score was Far Above, Above, Within Range of, Below, or Far Below their prediction based on student background. Those results are aggregated into a three-year SSM Performance Band. There are seven SSM Performance Bands: Far Above All Years, Above All Years, Within/Fluctuating, Below Most Years, Below All Years, Far Below All Years. The SSM calculation is based on API scores and publicly-reported student demographics, as reported to the California Department of Education with STAR testing.
The SSM attempts to identify how much value a school's educational program is adding to its students' performance. The SSM answers the questions: Based on what we know about how school performance varies by student demography, what is the predicted performance for a school given its student body, and is the school meeting or surpassing its predicted performance? These questions are answered using a linear regression model that controls for variables proven to influence academic achievement (e.g., parent education, socioeconomic status, etc.), resulting in an Annual School Performance Prediction. The SSM then compares that school's actual API score to the predicted API score based off of its demographic characteristics.
How does the SSM vary from CDE's Similar Schools Ranking?
While CDE uses both student and school variables in constructing the School Characteristics Index models, the SSM uses only student background variables that are outside of a school's control (e.g., income status, ethnicity) to calculate predictions for schools. The SSM does not include school structure variables, which are characteristics of the way a school chooses to operate (e.g., school calendar, class size, teacher credentialing, etc.), choices about which charters have a lot of autonomy. Given that the specific purpose of this metric is to establish a measure of minimum academic performance for charter schools, this more narrow set of independent variables is most appropriate. The SSM model was designed so as not to capture all of the variation in school performance (i.e., their best prediction), but rather only the variation caused by student population demographics (i.e., their base prediction).
The SSM is a relative measure of school performance, which complements other methods for understanding the spectrum of charter performance, such as those that look at actual performance and growth. CCSA recommends this system as an improvement upon current efforts in the identification of underperforming charters, but does not recommend it as the sole system for evaluating schools. The SSM is intended to flag consistently under-performing schools for a deeper review of additional measures of school performance, including status, growth and individual student progress metrics. CCSA believes chronically underperforming schools should undergo additional scrutiny before a renewal decision is made.
More information on the construction and intended use of the Similar Students Measure and the Annual School Performance Prediction is available in the Technical Guide to the Construction of the Annual School Performance Prediction (ASPP) and Similar Students Measure (SSM). Download the Technical Guide.
- Find more school data, tools and analysis of charter school performance in CCSA's "Portrait of the Movement" report.
- Learn more about our accountability work.
See a sortable list of where charter schools fall on CCSA's Accountability Framework, including SSM for: