Understanding Student Growth Percentiles (SGP)

Student Growth Percentiles (SGP) are one of the most common measures used by educators to assess student academic achievement. They can be found in many different state and national accountability systems, including Teacher and Leader Key Effectiveness System (TKES) and Learning Improvements Systems (LIAS).

The SGP is a simple measure of a student’s growth relative to academically-similar students. It is based on the percentile rank of a student’s current test score compared to his/her prior test score and is calculated in a variety of ways.

SGPs are estimated from standardized test scores and are prone to estimation errors (Akram, Erickson, & Meyer, 2013; Lockwood & Castellano, 2015; McCaffrey, Castellano, & Lockwood, 2015; Monroe & Cai, 2015; Shang, Van Iwaarden, & Betebenner, 2015). In addition, the resulting SGPs tend to be noisy measures of the “true” SGPs, defined as the student’s current latent achievement traits, which are a more accurate indicator of academic success.

True SGPs vary between students in classrooms taught by the same teachers (Lockwood & Castellano, 2014). For example, Grade 7 and 8 students may have significantly lower true SGPs for math than Grades 5 and 6 students. This is likely due to the higher within-subject, cross-year correlations of the latent achievement traits in these grades compared to earlier grades (Lockwood & Castellano, 2015; McFarland & Castallano, 2016).

Moreover, the variance of true SGPs can also be explained by contextual effects such as student-level factors related to student motivation, skills, or family circumstances that are correlated with observed student covariates. For example, in some neighborhoods, low SGPs for math are associated with poorer school performance; in other neighborhoods, high SGPs for math are associated with a more diverse student population.

These relationships between true SGPs and observed student covariates are more likely to be driven by contextual effects than by other factors that might lead to the development of an overly positive or negative association. However, they are important considerations when making policy decisions about the use of SGPs in an education system.

The SGP is used by stakeholders in many decision-making processes, such as the evaluation of teachers and schools. Its relatively easy to implement and manage makes it an excellent choice for educational systems that want to measure the impact of policies on student achievement.

SGPs are calculated using a two-step process. First, the data is prepared for analysis using a specialized software package. Then, the results are presented in a way that can be easily understood and interpreted by stakeholders who need to make decisions about the effectiveness of policies and programs. This process is intended to be as straightforward and easy as possible.