How we estimate percentiles: Georgia high school

A clear explanation of the data and the method, so you can judge how much weight to give the numbers.

What the data is

Every number here comes from official public test-results files: the Governor’s Office of Student Achievement (GOSA) downloadable data for the Georgia Milestones end-of-course (EOC) tests, and the Georgia Department of Education’s Georgia Insights data downloads. The tests are American Literature and Composition, Biology and United States History (2018, 2019 and 2021 to 2025), Algebra I and Coordinate Algebra (2018, 2019 and 2021 to 2023), Algebra: Concepts and Connections, the course that replaced Algebra I (2024 and 2025), and five tests Georgia gave only through 2019: Ninth Grade Literature and Composition, Geometry, Analytic Geometry, Physical Science and Economics. For each school, school district and the state, and for each test and year, these files report:

• the number of students tested and the number in each of the four achievement levels. Georgia hides a level with fewer than 10 students but still prints its percentage, and only one whole number of students fits that percentage and the number tested, so we fill it in exactly. We checked this on 2019, the one year GOSA published the same results twice, once with the small counts shown and once hidden: all 4,744 hidden counts came out exactly right; and
• the average score. The Georgia Department of Education publishes the average scale score of every school, district and the state (and from 2022 how spread out the scores are). We use Georgia’s own average wherever its count of testers closely matches GOSA’s, about 9 school results in 10. For the rest, the average is estimated from how the students split across the levels: the center of the bell curve that best matches the share of students below each level’s cut score.

Who is counted

These counts cover the whole school year: students who took the test in the December (winter) window are counted along with the spring testers. Georgia’s statewide totals here match the state’s own winter plus spring results to within 2% every year. Middle-school students who take a high-school course early, most often Algebra, take its end-of-course test and are counted here at their middle school (about one in five Algebra testers). Schools with fewer than 10 testers are not shown.

A course test is taken by whoever is in the course that year, so each test has its own group: about 144,000 students took Algebra: Concepts and Connections in 2025, and about 100,000 took US History. A percentile compares a score with that year’s takers of the same test, not with every student of the same age, and an Algebra percentile says nothing about Biology.

In 2021 only 55% to 62% of enrolled students took these tests, according to the Georgia Department of Education, so 2021 compares a smaller group than other years. The tool shows a note on those results.

How the percentile is estimated

Georgia publishes the exact scale-score range for each achievement level (for Biology, Proficient Learner is 525 to 608). Given a score, we:

1. identify which achievement level the score falls in;
2. count everyone in the lower levels as scoring below;
3. within the score’s own level, spread that level’s students along the group’s fitted curve (below) rather than evenly across the level’s range. Students bunch up toward the middle of the scale, so an even spread would put too many of them out at the far ends of the lowest and highest levels, which are very wide on these tests (Biology’s lowest level runs from 140 to 474).

That gives the percentile: the estimated share of students in the group who scored at or below the entered score.

About the smooth curve

The bell-like curve on each chart is a truncated-normal distribution centered on the group’s average score, with its spread set by Georgia’s published standard deviation where there is one (2022 to 2025) and otherwise fitted so that its area within each level matches the level counts. It’s there to visualize the shape of the group’s scores. The level counts set the headline percentile (steps above); the curve only decides where inside the student’s own level the line falls.

When a group’s students all sit in one or two levels, the counts can’t say how spread out their scores are. That is true of about one school result in twenty here. A curve that comes out too narrow is drawn no narrower than one fifth of the statewide spread, and inside the student’s level the percentile spreads that level’s students evenly instead.

Cut scores

Every Georgia end-of-course test has four levels: Beginning, Developing, Proficient and Distinguished Learner. On every test Developing starts at 475 and Proficient, the state’s proficiency line, at 525. The lowest score, the start of Distinguished and the highest score differ by test: Biology runs from 140 to 820 with Distinguished from 609, US History from 215 to 765 with Distinguished from 590. The score range for each level, by year, is on the score guides.

Algebra: Concepts and Connections was first given in 2023-24. In July 2024 a committee of Georgia educators kept the 475 and 525 cuts and set a new start for Distinguished, 580 (Algebra I’s was 594), and the State Board approved it that month; Georgia’s 2023-24 results are reported on it. So its share of Distinguished students does not line up with earlier Algebra I years. Percentiles compare students within one test and year, so they are not affected.

The ranges come from the Georgia Department of Education’s EOC Score Interpretation Guide for each school year (Table 2, or Table 1 in the older editions) and its 2017-18 and 2018-19 “Test Score Ranges and Cut Scores” sheets. The 2023-24 guide listed Algebra: Concepts and Connections as pending its standard setting; its ranges come from the 2024-25 guide.

The high-school progress report

The paid progress report puts every high-school test your child took in one table, with the percentile at each level from the school to the state, and charts each subject across the years.

• Each course exam is its own point. Every Georgia high-school test here is a course exam (such as Algebra or Biology), taken by the students in that course that year, a different group for each course, so the report does not join them with a line.
• Earlier years are compared statewide only. You can add your child’s grades 3-8 scores in the same subjects. The tool doesn’t know which middle school or district they attended, so those years are compared with every student in the state in that grade, not with this high school or its district.
• The report opens on the statewide view, the one level with a result for every test.

Limitations to keep in mind

• Percentiles are estimates, not official rankings. Treat a "62nd percentile" as "roughly the top 40%," not an exact standing.
• Small schools have small counts, so their estimates are noisier. Schools with fewer than 10 testers on a test are left out; the district and state results still count every student.
• In 2024, 82 students statewide who took Algebra: Concepts and Connections were counted as tested but given no achievement level. They are not in these counts.
• Not included: 2020 (no test, COVID); 2026 (GOSA has not posted it yet); Physical Science in 2021, when only 8th graders took it and Georgia’s score guide for that test could not be found; and the few students who still took Algebra I or Coordinate Algebra in 2024 or the five retired tests in 2021, which Georgia’s score guides for those years no longer list.
• Georgia is compared at the school, school district and state levels.

This site stores nothing you type. Scores are used only in your browser to draw your charts.