How we estimate percentiles: Maryland 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 Maryland State Department of Education assessment data for the high-school MCAP tests: Algebra I, Geometry, Algebra II and English 10 (2018, 2019 and 2022 to 2026) and Life Science (2022 to 2026). These files report, for each school, school system and the state, and for each test and year:

the percentage of students in each performance level and the real number tested; we turn the percentages into student counts. Where Maryland shows a small level only as “5.0% or less,” the count is worked out from the state's other published numbers: the levels add up to the number tested, Maryland also publishes how many students were proficient, and a school system's row and a school's all-grades row add up the rows under them. Every count rounds back to the percentage Maryland printed, 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.

Who is counted

These counts are not limited to the spring test: in every year MSDE's technical reports let us check (2023 to 2025), they also include the students who tested in winter. Middle-school students who take Algebra I or Geometry early are included, counted at their middle school.

A course test is taken by whoever is in the course that year, so the group changes from year to year: about 12,600 students took Geometry in 2026, against about 21,300 in 2025. 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 I percentile says nothing about Geometry.

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

Maryland publishes the exact scale-score range for each performance level (e.g. for Algebra I, Level 3 “Proficient Learner” is 750-774). 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. Checked against published statewide score distributions, this lands within about one percentile point of the true value for a typical score.

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 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. 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 ten here (mostly Algebra I and Geometry at schools whose students sit in two neighbouring levels) gets a wide default curve instead, which places a score inside its level close to an even spread.

Why estimates are still useful: the performance-level percentages are real for each group, and so is the number tested. The average score shown is estimated from how students split across the levels, and, as with every state, 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

Every test reports on a 650-850 scale. From 2022 MCAP has four levels (Beginning, Developing, Proficient and Distinguished Learner), with Proficient marking the state proficiency line, from 750:

Algebra I and Geometry: 650-724, 725-749, 750-774, 775-850;
Algebra II: 650-724, 725-749, 750-768, 769-850;
English 10: 650-724, 725-749, 750-775, 776-850;
Life Science: 650-730, 731-749, 750-771, 772-850.

In 2018 and 2019 these tests were reported on the earlier PARCC-era table with five levels (Did Not Yet Meet, Partially Met, Approached, Met and Exceeded Expectations), from 700, 725 and 750, with the top level starting at 805 for Algebra I, 783 for Geometry, 808 for Algebra II and 794 for English 10. Scale scores from those years don't line up exactly with later ones; percentiles do. The 2022 to 2026 ranges come from MSDE's MCAP cut-score table and its 2025-26 score interpretation guides (Life Science from Cognia's technical manual and its 2026 guide).

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.
Some school results are suppressed by the state (for privacy, small groups) and won't appear. In 2022 and 2023 Maryland also hid the split between the two lowest levels wherever 5% or fewer students were proficient. Those school results are left out (about a third of Algebra I schools in those two years); the school-system and state results still count every student.
Not included: 2020 (no test, COVID) and 2021 (a shortened test with no published high-school cut table); English 11 (2018 and 2019), the older high-school science test, and American Government.
Maryland is compared at the school, school system (its 24 local systems and the SEED School) and state levels.

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