It could be the test is just measuring different aspects of intelligence than the WPPSI or it could be that his IQ is actually dropping. Those preschool tests are not good predictors of IQ down the line...a very large percentage of kids who test high in preschool do not test high anymore several years later (and vice versa--some kids actually go up, like my DS, who was average at age 3 and went up 20+ points a couple years later --WPPSI to WISC). Google "Nurture Shock and gifted programs" for more info/research about testing young children.
