How we estimate percentiles: Nevada 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 Nevada Report Card, published by the Nevada Department of Education, for Nevada’s two high-school tests from 2018 to 2026: the ACT that every junior takes at school (its ELA and Math scores), and the Nevada High School Science test. For each school, school district and the state, and for each test and year, the Report Card gives:

• the number of students tested and the number of students in each of the four achievement levels, which add up exactly to the number tested, and
• from those counts, an estimated average score: the center of the bell curve that best matches the share of students below each level’s cut score. Nevada does not publish average scores for these tests.

Hidden numbers. To protect small groups, Nevada hides a group’s results entirely when it is very small. Those schools don’t appear, but they are few: the schools shown hold more than 99% of the test takers their districts report, except science in 2018 and 2019 (about 96%).

Who is counted

ACT ELA and ACT Math: every Nevada public school junior takes the ACT with Writing at school in the spring (state law requires it to graduate). The ACT ELA score is the average of the English, Reading and Writing scores, so a student needs the Writing test to have one, and slightly fewer students have an ELA score than a math score (about 1% fewer since 2019). In 2018 Nevada reported the same number of ELA and math testers for every district, so that year’s ELA count was made a little differently; the effect on the levels is at most about one percentage point.

High School Science: each student takes Nevada’s high-school science test once. Most take it in grade 9 and the rest in grade 10 (in 2026, about 33,000 ninth graders and 4,000 tenth graders), so a school’s science result counts everyone who took the test there that spring, in either grade. Results are by the school where the student tested, as the Report Card shows them.

The tests are taken by the whole class (about 34,000 students for ACT Math and 37,000 for science in 2026), so a percentile compares a score with Nevada public school students who took the same test that spring. It is not the same as the national rank on an ACT score report, which compares with test takers across the country. Students who took Nevada’s alternate assessment are not included.

The statewide row is Nevada’s own statewide total. In 2018 and 2019 that science total includes about 2,500 students (about 7%, mostly tenth graders) that no district reports. They scored lower than the rest, so in those two years the statewide science row has about one percentage point more students at Level 1 than the districts added together. From 2021 the districts add up to the state.

How the percentile is estimated

Nevada publishes the exact score range for each achievement level (e.g. for ACT Math, Level 3 is 20-25, and for science, Proficient is 450-513). 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.

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 fitted so that its area within each achievement 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. 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. About one school result in fifteen here gets a wide default curve instead, which places a score inside its level close to an even spread. Most of these are alternative and very small schools where every student scored in the two lowest levels, most often on ACT Math.

ACT scores are whole numbers from 1 to 36, and some levels span only a few of them (ACT Math Level 2 is 15 to 19). So a one-point change in an ACT score can move the percentile noticeably, and the curve is a smoothed picture of a score scale that really moves in steps.

Cut scores

Each test has four levels, and Levels 3 and 4 count as proficient. Nevada’s State Board of Education set the ACT levels on June 19, 2018: for ACT ELA, 2-11, 12-16, 17-23 and 24-36; for ACT Math, 1-14, 15-19, 20-25 and 26-36. Nevada names these levels by number only. Spring 2026 was the first year of ACT’s updated test for school testing, scored on the same 1-36 scale, and Nevada kept the same levels.

The Nevada High School Science test runs from 100 to 750, with four levels: Minimal Understanding 100-399, Partial Understanding 400-449, Proficient 450-513 and Advanced 514-750, set in summer 2017.

Both tables come from the Nevada School Performance Framework manual for each school year, from 2017-18 to 2025-26 (the 2025-26 edition is dated August 2026); every edition prints the same numbers. There is no 2020-21 edition, because Nevada paused its school ratings that year; the editions before and after it print the same table. The score range for each level, by 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.

• Lines join only the same kind of comparison. ACT ELA and ACT Math are grade 11 tests taken by the whole class. High School Science is taken once, in grade 9 or 10, so it is its own point.
• 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.
• Nevada hides the results of very small groups, so a few small schools don’t appear. Their students are still in the district and state results.
• Spring 2021 science was taken by about half the usual number of students (19,800), and spring 2022 by more than usual (49,500, including many tenth graders who had not tested in 2021).
• Not included: 2020 (no test, COVID) and Nevada’s alternate assessment.
• Nevada is compared at the school, district and state levels. Nevada’s school districts are its counties, so there is no separate county comparison.

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