Huckleberry, I may be in the minority here, but one of my dds had her WPPSI score (taken at 4.5) decrease significantly - across the board - when she was tested with the WISC in 2nd grade. She's also since then taken the WJ-III Test of Cognitive Abilities and it is more in line with her WISC score than her WPSSI, and her experiences in school lead me to believe the super-high WPSSI scores (for her) weren't accurate.
An IQ score contains signal and noise, and the noise is on average positive for the high scorers. Therefore some regression to the mean is to be expected. Is there research on how much?
SAT score reports indicate how the scores are likely to change upon retaking. A math SAT score of 770 falls on average to 745 upon retaking, but scores in the 500s on reading and writing change little upon retaking. So high scores mean-revert, but this phenomenon has little effect on middling scores.
