The phrase big data’ has been used to describe datasets that are too large for traditional analytical applications. However, the amount of data that is involved in SGP analysis is not quite at this level. It is a significant increase in scale but not an order of magnitude as great as, say, the number of Facebook interactions (Betebenner et al., 2014).
SGPs are computed using longitudinal data for students who have taken at least two tests in different testing windows. They provide a way to compare student achievement against the average performance of other students in the same grade level. This comparison is based on the assumption that students who have a higher score on the first test in a testing window will have a lower growth percentile on the second test.
To produce SGPs DESE uses up to five years of test score history for each student. This includes the Badger year in which students were allowed to take subject-specific math tests instead of a general grade-level 8th grade mathematics test. This information is used to produce SGPs in both ELA and math.
A variety of graphical displays can be produced associated with the SGP results. These can include graphs of student performance and charts displaying the growth of individual students. A list of charts and their corresponding code is available at the BAA Secure Site.
Another useful utility is the ability to compare the relative progress of one school or district against other schools and districts. This can help identify areas where additional work is needed to close gaps in achievement. It can also highlight areas where progress is particularly rapid and should be celebrated by teachers and administrators.
For example, a sixth grader named Simon achieved a 370 on the statewide English language arts (ELA) exam this year. He has improved his score by 70 points compared to his last year in fifth grade. In terms of his overall growth, this places him at the 74th percentile for sixth graders across the state. This is good news for Simon but it is important to keep in mind that many other sixth graders have achieved similar growth and his growth should not be exaggerated by too much.
As the use of SGPs continues to spread, it is essential that educators and policymakers understand how these tools are developed. The graphical displays and charts that are created are valuable but the underlying calculations should be fully understood. In addition, schools and districts should understand how to access the data they need to analyze and interpret SGPs. This will allow them to maximize the value of these tools for their improvement efforts.