My daughter consistently scores very high on ability and achievement tests; she is a DYS. My son had developmental delays that I initially didn't recognize because I only had my daughter for comparison. He no longer has delays and his teachers say he is very academically advanced, but even now he tests 30-40 points lower than her on IQ tests. It's possible he may have some exceptionalities affecting his scores, but there is clearly a big difference between them regardless.