13.1 Interpreting Standard Scores, Percentiles, and Stanines

13.1 Interpreting Standard Scores, Percentiles, and Stanines

Quick Answer: On norm-referenced tests with mean 100 and SD 15, a standard score of 100 is average; percentiles report relative standing (not percent correct); stanines 4–6 are average. CALT therapists must convert among these metrics and avoid overinterpreting a single score.

Psychoeducational reports rarely speak in raw points alone. Domain 4.E of the ALTA Competency Exam expects Certified Academic Language Therapists (CALTs) to interpret standard scores, percentile ranks, and stanines, then translate those numbers into instructional meaning for students with dyslexia and related language-based learning differences. Misreading a score can lead to the wrong placement, the wrong intensity of Multisensory Structured Language Education (MSLE), or false reassurance that a struggling reader is “fine.”

Why Norm-Referenced Metrics Matter in MSLE Practice

Formal dyslexia evaluations typically include measures of phonological awareness, rapid naming, decoding, orthographic knowledge, reading fluency, spelling, and listening/reading comprehension. Scores are almost always reported against a normative sample—peers of similar age or grade. Your job is not to recalculate every psychometric formula, but to know what each derived score communicates and what it does not.

Three ideas sit underneath nearly every report:

1. Relative standing — Where does this student fall compared with the norm group?
2. Distance from the mean — How unusual is the performance in standard-deviation units?
3. Confidence and pattern — Is one low score a reliable signal, or do you need converging evidence across subtests and informal work samples?

Standard Scores (Mean = 100, SD = 15)

Most cognitive and achievement batteries used in school and private psychoeducational evaluations (for example, Wechsler-linked achievement tests, WJ-style batteries, and many reading batteries) report standard scores with a mean of 100 and a standard deviation (SD) of 15.

A score of 100 means the student performed like the average peer in the norm group—not that the student answered 100% of items correctly. A score of 85 is about one SD below the mean; 70 is about two SDs below. Many state dyslexia guidelines and evaluation practices treat scores around or below the 16th percentile (roughly SS 85) as a flag for further analysis, but eligibility and therapy decisions are never based on one number alone.

Exam tip: If a stem gives mean 100 / SD 15 and a standard score of 100, the correct interpretation is average performance relative to norms—not mastery of the curriculum or grade-level “passing.”

Other Standard-Score Scales You May See

Not every instrument uses 100/15. Some subtests use scaled scores with mean 10 and SD 3. T-scores often use mean 50 and SD 10. Always read the publisher’s metric. On the CALT exam, if the question does not specify another scale, assume the common achievement metric of mean 100, SD 15.

Percentile Ranks

A percentile rank answers: “What percentage of the norm group scored at or below this student’s score?”

• 50th percentile ≈ average (median of the norm group)
• 25th percentile — the student scored as well as or better than 25% of peers; about 75% scored higher
• 16th percentile ≈ roughly one SD below the mean on a normal curve
• 2nd percentile ≈ roughly two SDs below the mean

Critical distinctions for Domain 4.E:

• Percentile ≠ percent correct. A student at the 9th percentile did not necessarily miss 91% of items.
• Percentiles are ordinal for interpretation of standing; equal percentile gaps are not equal skill gaps at every point on the scale.
• Very high or very low percentiles compress at the tails—small raw-score changes can swing percentiles near the extremes.

Stanines

Stanines (standard nines) divide the distribution into nine bands. Stanine 5 is the middle (average). Stanines 4, 5, and 6 are generally treated as the broad average band; 1–3 are below average; 7–9 are above average.

Stanines are coarser than standard scores or percentiles. They are useful for quick communication with families (“stanine 5 is average”) but less precise for fine-grained progress monitoring. If a report lists stanine 5, do not treat the student as “gifted” or “failing”—that band is average.

Putting the Three Metrics Together

A well-written report may say: word reading SS 78 (≈ 7th percentile, stanine 2). You should be able to recognize that all three metrics describe below-average relative standing. Conversely, SS 102, 55th percentile, and stanine 5 all point to average standing—even if classroom grades are poor for other reasons (fluency, written expression, attention, or inadequate instruction).

Confidence Intervals and Single-Score Caution

Every score is an estimate. Publishers provide standard error of measurement and often report a confidence interval (for example, SS 85 ± 5). A point estimate of 85 with a ±5 band means the student’s true score most plausibly falls somewhere between about 80 and 90. For CALT practice:

• Prefer patterns across phonological, decoding, spelling, and fluency measures over one subtest.
• Compare listening comprehension vs. decoding when applying the Simple View of Reading lens.
• Never tell a family a student “is a 78.” Speak in ranges, patterns, and instructional implications.

Common Interpretation Errors to Avoid

1. Confusing percentile with percent correct
2. Treating stanine 5 as a problem (it is average)
3. Assuming SS 100 means grade-level curriculum mastery
4. Ignoring oral language strengths when word reading is low (classic dyslexia profile cue)
5. Overweighting one outdated test date without current informal probes

CALT-Ready Translation Language

When you interpret scores for parents or teachers, pair the metric with a plain statement: “A standard score of 78 on word reading means performance well below the average of same-age peers—roughly the 7th percentile. That pattern, with stronger listening comprehension, is consistent with a need for intensive, systematic decoding and spelling intervention.” That sentence shows Domain 4.E skill: accurate metric literacy plus instructional meaning.

Mastery of standard scores, percentiles, and stanines is the gateway skill for the rest of Domain 4—using results for services, analyzing errors, and reading research that reports effect sizes alongside score metrics.