Assessment, Measurement, and Eligibility
Assessment items test whether you can select instruments, interpret scores correctly, and defend eligibility decisions. Illinois expects a comprehensive, non-discriminatory evaluation using multiple methods, with the school psychologist integrating norm-referenced, curriculum-based, observational, and rating-scale data.
Score interpretation
- Standard scores: mean 100, SD 15; a score of 85 is one SD below the mean, percentile rank 16.
- SEM and confidence intervals: report a band, not a point. A 95% interval is approximately the score ± 1.96 × SEM.
- Many rating scales use T-scores (mean 50, SD 10). Percentiles are not equal-interval, so never average them.
- Floor and ceiling effects distort extreme scores; check the manual's norms and the examinee's fit to them.
Eligibility and classification
- IDEA categories include specific learning disability, other health impairment (ADHD often qualifies here), autism, emotional disability, intellectual disability, and speech/language impairment.
- SLD identification may use RTI or a pattern of strengths and weaknesses; a severe discrepancy alone is not required and cannot be the sole criterion.
- Exclude lack of appropriate instruction and limited English proficiency as the determinant factor.
- Adaptive behavior must be assessed when intellectual disability is suspected.
Accuracy concepts
Sensitivity (true positives), specificity (true negatives), and base rate determine positive predictive value. When a condition is rare in a classroom, even a good screener yields many false positives.
Worked example
A student earns 82 with an SEM of 3. The team asks whether the true score is below 85. The 95% interval is 82 ± 5.9, or about 76–88, which includes 85. The score is not statistically distinguishable from the cutoff, so eligibility must rest on other evidence.
Traps
Averaging percentiles; treating a single subtest as diagnostic; ignoring the referral question; and applying English-only norms to a student educated in another language.