How we estimate percentiles: Illinois 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 the Illinois Report Card published by the Illinois State Board of Education (ISBE), read from the same results service the Report Card website uses. It covers the SAT that Illinois gave every 11th grader from 2018 to 2024 (there was no test in 2020), and the tests that replaced it in spring 2025: the ACT in 11th grade, the PreACT Secure in 10th grade and the PreACT 9 Secure in 9th grade, for 2025 and 2026. For each school, district and the state, ISBE reports:

the percentage of students in each performance level and the number tested; we turn the percentages into student counts. In 2026 ISBE stopped printing any level that holds fewer than 10 students. For those rows we work out the hidden levels from the percentages ISBE does print (the levels have to add up, and each hidden level is 0 to 9 students). When a row's hidden levels could add up in very different ways, we leave that school or district out for that test rather than guess. For the smallest groups ISBE prints only the share of students who are proficient, which is not enough to place a score, so those are left out too, and
from those figures, an estimated average score: the center of the bell curve that best matches the share of students below each level’s cut score. ISBE also publishes a real average score for the SAT and for the 11th-grade ACT. We use it to check our estimate. For most schools our estimate lands within a few points of ISBE’s SAT average, and within half a point of its ACT average, in every year. Where most of a school’s students are in the lowest SAT level our estimate runs lower than ISBE’s average, because that level covers a wide range of scores (200 to 420 or 440).

Who is counted

SAT (2018 to 2024): the 11th graders who took the SAT in school that spring and received a valid score. Reading and Writing is the SAT’s Evidence-Based Reading and Writing section score; Math is the Math section score. Some 12th graders (about 2,000 to 7,000 a year) also took it because they had no valid 11th-grade score. They are not counted here. (From 2022, ISBE’s own spreadsheet download adds them to its school, district and state figures, so its percentages for those years can differ slightly from the ones here.)

From 2025: the 11th graders who took the ACT, the 10th graders who took the PreACT Secure and the 9th graders who took the PreACT 9 Secure that spring, each counted in its own grade. Students who take the alternate assessment (DLM-AA) are not included in any of these tests.

Important: the public data does not contain individual student scores, only these group summaries. So no tool can compute a true rank of one student against every other student. What we provide is a well-grounded estimate.

How the percentile is estimated

Illinois publishes the score range for each performance level (e.g. for the SAT Math section, Meets Standards is 540-660; for the 11th-grade ACT Math test, Proficient is 19-27). Given a score, we:

identify which performance level the score falls in;
count everyone in the lower levels as scoring below;
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.

That gives the percentile: the estimated share of students in the group who scored at or below the entered score. SAT section scores come in steps of 10 (450, 460, 470 and so on), and ACT scores are whole numbers, so enter the score exactly as it appears on the score report.

About the smooth curve

The bell-like curve on each chart is a truncated-normal distribution fitted so that its area within each performance level matches the level counts, centered on that estimated average score. 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, and the fitted curve can come out far too narrow. Those curves are drawn no narrower than one fifth of the statewide spread, which is about the size of the test's own measurement error, and inside the student's level the percentile spreads that level's students evenly instead.

Why estimates are still useful: the performance-level percentages are real for each group. The average score shown is estimated from how students split across the levels, and the only other assumption is how scores are distributed inside a level, a small and bounded range. Across a whole school, district, or the state, that assumption averages out well, so the comparison ("above/below average here vs. statewide") is reliable even though the exact percentile is approximate.

Cut scores

SAT (2018 to 2024). ISBE set four performance levels on the two SAT section scores after the spring 2017 test: Partially Meets, Approaching, Meets and Exceeds Standards. Meets Standards starts at 540 in both sections. The same ranges applied every year through 2024, including the 2024 digital SAT: ISBE’s May 2024 score webinar prints the same table as its 2017 performance-level FAQs and its SAT Performance Levels chart.

ACT, PreACT Secure and PreACT 9 Secure (2025 on). For spring 2025 Illinois adopted new performance levels shared by all its state tests: Below Proficient, Approaching Proficient, Proficient and Above Proficient, with separate ranges for each grade’s test and subject. Sources: ISBE’s “ELA, Math and Science Cut Scores and Score Ranges” (August 2025), still ISBE’s current tables when the 2026 results came out.

The score range for each level, by test and year, is on the score guides.

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 subject is a line. Every Illinois high-school test here is a grade-level test, taken by every student in that grade, so a subject’s results line up across the years. The SAT (through 2024) is its own subject, separate from the ACT tests that replaced it.
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. Groups of fewer than 10 students are not published.
The SAT and the ACT are different tests on different score scales. A percentile compares a score with other students who took the same test in the same year, so an SAT result from 2024 and an ACT result from 2025 are each fair within their own year, but the scores themselves can’t be compared.
In 2026 some small schools and districts are missing for a test because ISBE hid too many of their levels to work them out (see above).
There are no 9th- or 10th-grade results before 2025. Illinois gave the PSAT 8/9 and PSAT 10 in those years, but ISBE’s public report-card data does not include their results.

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

Back to the tool