GreatPhillySchools Ratings Methodology

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(Updated April 2017)
 

GreatPhillySchools (“GPS”) compares schools serving similar grade levels to one another: elementary and middle schools (K-8) or high schools (9-12) using various data sources. We weigh the each of the ratings differently depending on the school type.

Elementary and Middle Schools (Grades K-8):
  • Academics: 60% (30% math and 30% reading)
  • Attendance: 30%
  • Safety: 10%
High Schools (Grades 9-12):
  • Academics: 30% (15% math and 15% reading)
  • College-Bound: 30%
  • Attendance: 20%
  • Safety: 20%

Note: Schools are categorized based on the highest grade level in the school. For example, a school serving grades 6 through 12 would fall in the "High Schools" category.  

For more detail on the data sources used to determine school ratings, see GPS Data Sources.

Ratings Scale

Schools are given ratings on a scale between 1 to 10 based on their decile ranking. Specifically, GPS uses interval-based deciles to produce ratings. Unlike traditional deciles that require forced differentiation between schools with similar performance, interval-based deciles allow for cut points defined by the range of existing school performance, while maximizing grouping for schools with similar performance.

GPS uses two variations of interval-based deciles:

  • Equal Interval Deciles: The range between the highest-performing school and the lowest-performing school is divided into 10 equal tiers based on the performance metric. Any two schools with the same relative gap in performance will have a similar relative gap in performance tier. Equal interval deciles are used for GPS’ overall and sub-ratings (e.g., Academic, Attendance, College Bound).

  • Logarithmic Interval Deciles: The range between the highest-performing school and lowest-performing school is divided into 10 exponentially increasing size tiers based on the performance metric. Any two schools with the same relative exponential difference in performance will have a similar relative gap in tier. Logarithmic interval deciles are used for GPS’ Safety ratings.

  • pie charts for ratings methodology
Academic Sub-Ratings

Math: This rating represents the percentage of students performing at or above grade level in math, as measured by the most recently available standardized test data. The raw score is then compared to other schools in Philadelphia using equal interval deciles. See Data Sources for information about standardized test data sources.

Reading: This rating represents the percentage of students performing at or above grade level in reading, as measured by the most recently available standardized test data. The raw score is then compared to other schools in Philadelphia using equal interval deciles. See Data Sources for information about standardized test data sources.

GPS then creates a list of all schools sorted by their proficiency scores for both subject areas tested from highest to lowest. A mathematical formula is used to sort those schools into 10 groups with equal increments between them, known as deciles. The highest-performing group of schools at the top of that list is assigned a “10”, the next group assigned a “9”, and so on.

GPS ratings are comparative -- meaning a school that is assigned a “10” represents the highest performing amongst all Philadelphia schools; likewise, a school that is assigned a “1” represents the lowest performing amongst all Philadelphia schools. For example, a school assigned a “10” in reading does not mean that 100% of their students performed at or above grade level in reading in the most recent standardized test. Instead, a “10” rating means the school is ranked in the top group of all Philadelphia schools for their reading score.

Comparing Academic Performance Between Public and Catholic Schools

All elementary and middle school students (grades K-8) enrolled in public and public charter schools take the Pennsylvania System of School Assessment (PSSA) exam in various subjects. The PSSA is a standardized, criterion-referenced exam primarily designed to assess grade-level proficiency in Math and English Language Arts. Students enrolled in Catholic schools take the TerraNova exam -- a standardized, norm-referenced assessment primarily designed to assess student performance relative to all other TerraNova test-takers.

GPS built a model to predict a student’s likely PSSA performance based on their TerraNova performance. This was done by comparing performance amongst a group of students that took both exams, allowing for the most accurate comparison of student performance across the Catholic schools and public schools.

Non-Academic Sub-Ratings

Attendance: This rating represents the Average Daily Attendance (ADA) rate for the school. ADA data for all schools is sorted from highest to lowest, then the same deciling methodology described above is applied to produce ratings on a scale of 1 to 10.

Safety: This rating represents the safety and/or discipline incident count per 100 students. We calculate this rating based on the number of safety and/or discipline incidents reported by schools (see data sources for more information).

Calculation

Each school’s total incident count is divided by 100 students in order to calculate an incident rate comparable across schools with various student enrollment. For example, a school with 1,000 students and 20 incidents has an incident rate of 2-per-100 students, while a school of 300 students and 9 incidents has an incident rate of 3-per-100. Incident Count data for all schools is then sorted from highest to lowest, divided into ten different groups, then assigned safety ratings on a scale of 1 to 10.

Unlike other rating categories, the groups for safety ratings are established on a logarithmic scale, rather than in equal-sized increments, meaning each successive increment is exponentially larger. This allows for greater articulation of differences at the low end of the scale. On an Equal Interval decile scale, a school with four incidents per 100 students might be rated the same as a school with one incident per 100, even though that represents four times as many incidents. A 10 rating for safety means a school fell into the band of schools with the fewest number of incidents per 100 students. 

College Bound: This rating represents the percentage of annual graduates who enroll in any postsecondary institution in the first fall following their graduation date. Schools are then divided into equal-sized groups to create ratings from 1 to 10, with 10 representing the highest college enrollment rates.

Overall Quality: This rating represents a combination of each school’s academic, college bound (for high schools), attendance, and safety ratings. The data is combined into one master list ranked by weighted formulas (see below). Schools are then grouped in deciles from 10 to 1 in equal increments to produce an overall rating.

Categories Not Factored Into Overall Ratings

High School Graduation Rates: For public high schools, this statistic is listed on each school’s profile page. It represents the school’s four-year “cohort” graduation rate, which is tracked by the state. The cohort rate represents the percentage of 9th graders who graduate from the same school four years later, after subtracting out students who transferred to other schools and adding in those students who transferred in.

Achievement Gap: This rating represents the proficiency gap between students classified as “economically disadvantaged” and those not classified as economically disadvantaged. Only public schools with at least 40 students in each of these subgroups receive an achievement gap rating.

The achievement gap is calculated as the number of percentage points between the two groups on the average academic proficiency score described above. Then all schools receiving a gap score are ranked from highest to lowest, then groups are sorted using the same method. Note: this rating is listed on applicable school profiles; however, it is not factored into overall ratings.

Disclaimer: Data collection and analysis for GPS was managed by the Philadelphia School Partnership in consultation with Data Partners LLC, a data analytics consulting firm with significant experience analyzing and modeling student and school performance data. Guidance and assistance was also provided by the Pennsylvania Department of Education, McGraw-Hill’s CTB division (producer of the TerraNova) and Frontier 21 Solutions, an education research company.

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