November 10, 2023

SGP Data Interpretation and Validation

When implementing a SGP system it is important to understand the implications of the many technical choices that can be made. These choices affect the interpretation and validity of student growth data that is reported to stakeholders. This article is intended to describe a few of these choices and to provide guidance for navigating the many options.

The most important decision is whether to format the data in WIDE or LONG format. In general, the lower level functions studentGrowthPercentiles and studentGrowthProjections require the data to be in WIDE format whereas the higher level wrapper functions (studentInstructorLookup, etc) require it to be in LONG format. For most SGP analyses we recommend formatting the data in LONG format, as this provides numerous preparation and storage benefits over WIDE format.

Choosing which student growth trajectories to use is another important choice that affects the resulting estimates and projections. SGP systems usually utilize the historical growth trajectories of Star examinees to determine their current status and to project their progress towards proficiency over time. These trajectories are correlated with various student covariates including gender, race/ethnicity, and home language.

It is important to understand that, as a consequence of these correlations, true SGPs are likely to be related to the background characteristics of students who are in a given classroom. This is an unavoidable consequence of using a statistical model to estimate student growth. Specifically, students with more or less background characteristics will be expected to have different true SGPs than students with similar backgrounds.

SGPs are often used to evaluate the effectiveness of a program. Ideally, SGPs are aggregated using the median so that a program’s score is not influenced by a small number of students who can’t keep up with their classmates. A program is considered to be at risk of this problem if more than 5% of students have SGPs that are 50 points or more below the class median.

It is also possible to use the SGPs for individual students to evaluate the effectiveness of a teacher or a particular instructional method. This can be done by selecting a prior or current year during the report customization process and viewing each students window specific SGPs. This can help to identify teachers that are having a negative impact on the progress of students within their classrooms. These are typically instructors that have a high proportion of slow learners or students with other barriers to learning. Fortunately, there are many instructional practices and supports that can be implemented to help these students improve their academic performance. These practices include individualized support, enrichment opportunities, and the use of different learning modalities. A good teacher can make a significant difference in the achievement of these students. This is why a quality educator is one of the most valuable investments a district can make.