How we estimate percentiles

Plain-English 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 California CAASPP research files (Smarter Balanced, ELA & Math, grades 3-8). These files report, for each school / grade / year:

the number of students tested and their mean scale score (real, reported figures), and
how many students landed in each performance level, a real, reported count for 2024 onward. For 2022-2023, CAASPP’s file published percentages instead, which we convert directly to counts (percentage × number tested).

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

How the percentile is estimated

California publishes the exact scale-score range for each performance level (e.g. for Grade 3 Math, Level 4 “Standard Exceeded” is 2501-2621). Given your child's 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, use linear interpolation across that level's count, assuming scores are spread evenly across the level's range.

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 real reported counts, anchored to the group’s real reported mean. It's there to visualize the shape of the group's scores. The headline percentile comes from the counts (step above), not from the curve.

Why estimates are still useful: both the performance-level counts and the mean score are real, reported figures. The only assumption anywhere in this pipeline is how scores are distributed inside a level, a small and bounded range. Across a whole school, district, county, 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.

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/grade cells are suppressed by the state (for privacy, small groups) and won't appear.
Smarter Balanced scale scores run roughly 2000-2800 (the range varies by grade) and are stable across years. No statewide test was given in 2020 or 2021 (COVID).
Charter schools appear as their own districts in the state files and are included in the school, district, county and statewide comparisons.

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

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