Similar Students Measure (SSM)
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.
How is the SSM calculated?
The Similar Students Measure (SSM) helps to set a minimal bar of performance that allows for uniformly high expectations while taking into account students' background. The SSM is used as one component of CCSA's Minimum Criteria for Renewal, which also include status, growth, and post-secondary readiness. CCSA's Minimum Criteria do not attempt to measure quality or supersede any performance goals set by the state or federal government. These criteria are only meant to determine which charters have academic outcomes that warrant renewal and which charters do not.
Each year, schools are placed in one of five SSM categories:
- Far Above = actual score at least 2 standard deviations above predicted score
- Above = actual score 1 to 2 standard deviations above predicted score
- Within = actual score within 1 standard deviate of predicted score
- Below = actual score 1 to 2 standard deviations below predicted score
- Far Below = actual score at least 2 standard deviations below predicted score
When possible, these results are aggregated into a three-year SSM Performance Band. There are seven possible Bands: Far Above All Years, Above All Years, Within/Fluctuating, Below Most Years, Below All Years, Far Below All Years.
The SSM attempts to identify how much value a school's educational program is adding to its students' performance. The SSM answers two questions:
- What is the predicted performance for a school given its student body?
- To what extent is the school missing or surpassing its predicted performance?
These questions are answered using pairs of linear regressions for each grade and subject. The regressions control for variables that influence academic achievement (e.g., parent education, socioeconomic status, race/ethnicity, etc.). Actual achievement minus predicted achievement produces a raw SSM score. After averaging ELA and Math in each grade, we weight by the number of valid scores per grade to obtain one number for each school. These school-level SSM scores allow us to place schools in the categories described above as well as in 20 equal bins. The more nuanced bins allow CCSA to analyze charter performance in a relatively fine-grained manner.
The SSM calculation is based on publicly-reported achievement scores and tested-student demographics, as reported to the California Department of Education. CCSA does not produce SSM categories for schools that are ASAM, Alternative, or have fewer than 30 valid scores.
The 2016-17 CCSA Technical Guide is now available, where you can find more information on the construction and intended use of the Similar Students Measure.
Learn more about the methodology behind our SSM:
- CCSA Joint Commentary with Fordham Institute
- 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.
- Read CCSA's response to Ohio State University article on SSM
See a sortable list of where charter schools fall on CCSA's Accountability Framework, including SSM for:
More Accountability Resources
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