Private Evaluation vs School Testing: Why the Scores Are Different

This Happens More Than You Think

You paid for a private psychoeducational evaluation. The private evaluator diagnosed your child with a specific learning disability. You brought the report to the school. The school ran their own testing — and their scores are higher. Now the school says your child does not qualify for services based on their results, and you are sitting in an IEP meeting with two reports that seem to contradict each other.

This score discrepancy between private and school evaluations is one of the most common and most distressing situations parents face. But the scores are not contradicting each other. They are measuring the same child under different conditions, often with different instruments and different norming comparisons — and understanding why they diverge is the key to advocating with both reports effectively.

Why the Same Child Gets Different Scores

Different Test Batteries

The most straightforward explanation: the school and the private evaluator used different tests. Schools frequently use the Woodcock-Johnson because it is co-normed with cognitive and oral language batteries, making it efficient for comprehensive evaluations. Private evaluators often use the WIAT-4 or KTEA-3, which offer features like the Dyslexia Index, Error Analysis, and co-linking with the WISC-V.

These batteries test the same academic domains but use different items, different scoring rubrics, and slightly different constructs. WIAT-4 Reading Comprehension uses multiple-choice and open-ended questions about longer passages. Woodcock-Johnson Passage Comprehension uses a cloze (fill-in-the-blank) format with shorter passages. A child who excels at context-based guessing will score higher on the WJ format. A child who is a careful, methodical reader might score higher on the WIAT-4 format.

Small differences in construct and format routinely produce 5-10 point score differences on the same child. This is expected measurement variation, not evidence that one test is wrong.

Different Norming Comparisons

Age norms versus grade norms can shift scores significantly, especially for children who are old or young for their grade. A child who was retained and is now a year older than their classmates will look different when compared against age peers (children their age with one more year of instruction) versus grade peers (children in the same grade with the same instructional exposure).

If the school used grade norms and the private evaluator used age norms — or vice versa — the standard scores can diverge by 5-15 points without either test being wrong. Check the norming basis on each report. It is usually noted in the score tables or the methodology section.

Different Testing Conditions

Private evaluations happen in a quiet, child-friendly office with a clinician who specializes in assessment. The session is scheduled at the child's optimal time, breaks are taken as needed, and the evaluator observes behavioral cues and adjusts accordingly. Some private evaluations are split across two or three sessions to prevent fatigue.

School evaluations happen in a school building — often during the school day, sometimes pulled from a class the child enjoys, sometimes in a noisy resource room. The school psychologist may be managing a caseload of 60+ students and conducting the evaluation in a single session. Testing at 2:00 PM after a full day of school produces different results than testing at 10:00 AM in a calm office after a good breakfast.

These conditions do not make the school's results invalid. But they may explain why the school's scores are higher (a child trying harder in a familiar, lower-pressure setting) or lower (a fatigued, anxious child performing below their capability).

Practice Effects

If the school and the private evaluator administered the same test battery within a few months of each other, the second administration may show inflated scores due to familiarity with the test format and specific items. Standard achievement batteries are designed to be administered no more than once per year to avoid practice effects. If your child took the Woodcock-Johnson at school in September and the same Woodcock-Johnson privately in November, the second set of scores is contaminated by test familiarity — those gains are not real skill improvements.

How to Use Both Reports at the Meeting

Under IDEA in the United States, the school is required to consider outside evaluations. They do not have to adopt the private evaluator's conclusions, but they cannot ignore the report. Here is how to present both reports effectively:

Focus on the pattern, not the number. If the private WIAT-4 shows Word Reading at 94 and Pseudoword Decoding at 72, and the school's WJ shows Letter-Word Identification at 98 and Word Attack at 79, both evaluations are telling the same story: sight-word reading is average, phonological decoding is significantly below average. The exact numbers differ, but the pattern — the gap between real-word reading and decoding — is consistent.

Line up the subtests. Create a side-by-side table mapping the equivalent subtests from each battery. The Achievement Test Decoder includes a cross-battery comparison table for exactly this purpose: WJ Letter-Word Identification maps to WIAT-4 Word Reading maps to KTEA-3 Letter & Word Recognition. When you align them, the convergent patterns become visible even when the absolute scores differ.

Ask about the conditions. Ask the school psychologist: "What time of day was my child tested? Was the evaluation completed in one session or multiple? Were breaks offered?" Document the answers. If the private evaluator's behavioral observations note good engagement, optimal testing conditions, and rapport — while the child was tested at school after lunch in a single three-hour session — the conditions may explain some of the score differences.

Request reconciliation. You can ask: "Given that we have two evaluations with somewhat different scores but consistent subtest patterns, can we discuss what the convergent findings tell us about my child's needs rather than choosing one report over the other?"

In the UK, Canada, and Australia

In England, local authorities sometimes dismiss private Educational Psychologist reports when they conflict with school-based assessments. The SEND Code of Practice requires the local authority to consider all evidence, including private reports. If the private report identifies needs the school report does not, request that the local authority explain in writing why they disagree with the private findings.

In Ontario, IPRC committees must consider information about the pupil submitted by a parent, though they are not bound by a private report's conclusions. The private report is particularly powerful when the public school board's assessment waitlist has delayed evaluation by 2-4 years — the private data is more current.

In Australia, school-based and private assessments can provide context about a student's needs, but an achievement-test score does not determine an NCCD adjustment level or NDIS funding. NCCD levels are based on documented adjustments and support, while NDIS funding depends on whether requested supports meet NDIS criteria and address disability-related functional needs. The school system is responsible for supports whose main purpose is learning or education outcomes.