CELF-5 core, PLS-5, GFTA-3
Optional: SEM from the test manual for the confidence interval.
Converted scores
- Percentile rank
- 16
- Standard score (100/15)
- 85
- Scaled score (10/3)
- 7
- T-score (50/10)
- 40
- z-score
- -1
- SD below mean
- 1
Within normal limits
At or above the 16th percentile.
95% confidence interval (standard score): 77–93. Report this range in your evaluation rather than a single point estimate.
Quick reference table
| Standard score | Scaled | T-score | z | Percentile |
|---|---|---|---|---|
| 130 | 16 | 70 | 2 | 98 |
| 115 | 13 | 60 | 1 | 84 |
| 110 | 12 | 57 | 0.67 | 75 |
| 100 | 10 | 50 | 0 | 50 |
| 90 | 8 | 43 | -0.67 | 25 |
| 85 | 7 | 40 | -1 | 16 |
| 78 | 5.6 | 35 | -1.47 | 7 |
| 70 | 4 | 30 | -2 | 2 |
| 55 | 1 | 20 | -3 | <1 |
How to use converted scores in a report
Conversions assume a normal distribution, which is how most norm-referenced speech and language tests are scaled. That assumption breaks down at the tails, so treat percentiles below 1 or above 99 as approximate and defer to the exact percentile printed in the test manual when one is available. Also confirm the metric before converting: a CELF-5 subtest score of 7 is a scaled score, not a standard score, and mixing the two is the single most common scoring error in draft reports.
Confidence intervals matter more than most reports acknowledge. A standard score of 78 with an SEM of 4 spans roughly 70 to 86 at the 95% level, which crosses two common eligibility thresholds. Reporting that band, along with observational and curriculum-based data, protects the team from over-reading a single number.
Related resources
FAQ
What percentile is a standard score of 85?
On a test with a mean of 100 and a standard deviation of 15, a standard score of 85 is exactly one standard deviation below the mean, which corresponds to the 16th percentile. That means the child scored at or above roughly 16% of same-age peers in the normative sample.
What standard score qualifies a student for speech services?
Eligibility criteria are set by each state and district, but common thresholds are 1.5 standard deviations below the mean (standard score 78 or below on a 100/15 test) or 2 standard deviations below the mean (standard score 70 or below). Test scores are only one part of eligibility — adverse educational impact and clinical judgment also apply.
How do I convert a scaled score to a standard score?
Scaled scores use a mean of 10 and a standard deviation of 3, so convert to a z-score first with (scaled - 10) / 3, then multiply by 15 and add 100. A scaled score of 7 is one standard deviation below the mean, equal to a standard score of 85 and the 16th percentile.
Should I report percentile ranks or standard scores?
Report both. Standard scores support eligibility decisions and comparisons across subtests, while percentile ranks explain performance to families in plain language. Include a confidence interval whenever the test manual provides one, because a single point estimate overstates precision.