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iReadyScores

Our Methodology

Last updated: May 2026

Our Methodology explains how iReadyScores.com converts published i-Ready norms into percentile lookups and placement-level guidance without inventing unpublished cut scores.

Data Source

All percentile data comes from Curriculum Associates' publicly available i-Ready Diagnostic National Norms documents. These are released annually and describe the distribution of scale scores for students across the U.S. who took the diagnostic during each school year.

We manually transcribe the norm tables into structured JSON data files and validate each value against the source document. Where multiple sources are available (e.g., prior-year published norms used as cross-reference), we verify for consistency.

Percentile Lookup Algorithm

Curriculum Associates publishes norms at specific percentile points: the 1st, 5th, 10th, 15th, 20th, 25th, 30th, 35th, 40th, 45th, 50th, 55th, 60th, 65th, 70th, 75th, 80th, 85th, 90th, 95th, and 99th percentiles for each grade, subject, and season.

When a user enters a scale score that falls exactly on one of these published points, we return that percentile directly.

When a score falls between two published points (the common case), we use linear interpolation to estimate the most accurate percentile: 

percentile = lo_pct + (score - lo_score) / (hi_score - lo_score) × (hi_pct - lo_pct)

This is the standard interpolation method and produces results consistent with the full cumulative distribution within the published bounds. The result is rounded to the nearest whole number.

Placement Level Calculation

i-Ready uses five placement levels: Well Below Grade Level, Below Grade Level, On Grade Level, Above Grade Level, and Well Above Grade Level. Curriculum Associates publishes the exact scale-score boundaries for each level by grade and season.

We use these published boundaries to classify any score into the appropriate placement level. We do not estimate or extrapolate placement boundaries — only the officially published ranges are used.

Limitations

  • Interpolation is an estimate: Linear interpolation assumes a roughly uniform distribution of scores between percentile points. The actual distribution may vary, so interpolated percentiles should be understood as close approximations, not exact values.
  • Annual norm updates: Norms are updated each school year. We update our data files as quickly as possible after new norms are released, but there may be a brief lag. Each page is labeled with the school year the data applies to.
  • This site is for reference only: Educators and parents should use the official i-Ready student report provided by their school for any official or instructional decisions. Our calculator is a convenience tool, not a substitute for official reporting.

Corrections and Feedback

If you believe any data on this site is incorrect, please cross-reference with the official Curriculum Associates norms document for the applicable school year. Verified corrections are applied promptly. Questions and verified corrections can be sent to hello@ireadyscores.com.