Student Growth Percentiles

Growth models use longitudinal assessment data to monitor the progress of students and schools. The Student Growth Percentile (SGP) model describes how well a student performed relative to peers with similar score histories. SGPs provide a normative measure of growth, describing growth relative to other students. SGPs can be used to address important questions such as:

• How much growth is needed to become on target for college and career readiness?
• How did my student’s growth compare to other students nationally?
• How much does growth in my school vary across subject areas, grade levels, and student subgroups?
• Has growth at my school improved over time?
  

Resources for SGPs are provided for the PreACT Suite of assessments and the ACT test. The resources provide a means to measure growth across grade levels and assessments. An SGP “lookup” table is provided here for the following combinations of assessments and time periods: 

• PreACT 8/9 to PreACT 8/9, Grade 8 to Grade 9
  
• PreACT 8/9 to PreACT, Grade 9 to Grade 10
• PreACT 8/9 to PreACT Secure, Grade 9 to Grade 10
• PreACT to ACT, Fall Grade 9 to Spring Grade 11
• PreACT to ACT, Spring Grade 9 to Spring Grade 11
• PreACT to ACT, Fall Grade 10 to Spring Grade 11
• PreACT to ACT, Spring Grade 10 to Spring Grade 11
• PreACT Secure to ACT, Spring Grade 10 to Spring Grade 11

The SGP lookup table provides the SGP value (ranging from 1 to 100) associated with each combination of current-year test score and prior-year test score. For example, suppose a student scored 16 on the grade 10 PreACT Science test and 21 on the grade 11 ACT Science test one year later. Their SGP would be 87 (as shown in the image below, which is an excerpt from the 2024 SGP lookup table).

The SGPs are updated periodically to reflect the most recent longitudinal data from ACT assessments. The SGPs are estimated using quantile regression methods (Koenker, 2005) by the SGP R package (Betebenner, VanIwaarden, Domingue, Shang, 2014). The SGPs are based on large samples of students from across the country who tested in recent years through school-day testing programs. The samples are weighted to be more representative of the population of students who take the ACT with respect to student demographics (race/ethnicity and gender), school poverty level, school type (public or private), and school mean ACT score. Table 1 summarizes the samples used to estimate the SGPs for English, math, reading, science, STEM, English + Reading, and Composite scores with and without science. 

Table 1. SGP Sample Summary

Table 2 summarizes the samples used to estimate the SGPs for ELA. Note that the ELA samples are smaller because students must take the ACT Writing test to have an ELA score. For ELA, the ACT ELA score is used as the current test score and English + Reading is used as the prior test score.

Table 2. ELA Sample Summary

The SGP lookup table includes the following fields (columns):

• version is the year that the table was updated. For example, the 2023 version used data collected through spring 2023.
  
• prior_assessment is the name of the test used for the prior year to establish the baseline for measuring growth (PreACT 8/9 or PreACT).
• current_assessment is the name of the test used for the current year to measure the growth endpoint (PreACT 8/9, PreACT, or ACT).
• prior_grade is the grade level when the prior assessment was administered.
• current_grade is the grade level when the current assessment was administered.
• growth_period describes the period of time between the prior test and current test.
• subject is the name of the test or combined test score (English, mathematics, reading, science, STEM, Composite, or English+Reading).
• prior_score is the test score earned on the prior year assessment.
• current_score is the test score earned on the current year assessment.
• sgp is the estimated Student Growth Percentile.
• growth_level indicates the growth quartile (1 for SGP values from 1-24, 2 for SGP values from 25-49, 3 for SGP values from 50-75, 4 for SGP values from 76-100).

The SGP lookup tables can be used to derive SGPs for individual students or can be imported into school information systems to permit additional research on student growth.

References

Betebenner, D.W., VanIwaarden, A., Domingue, B., and Shang, Y (2014). SGP: An R Package for the Calculation and Visualization of Student Growth Percentiles & Percentile Growth Trajectories. R package version 1.2-0.0. URL.

Koenker, R. (2005). Quantile Regression. New York, NY: Cambridge University Press.