Jennifer Senior carefully explains why IQ tests for toddlers are worthless, or worse. David Shenk highly recommends the article:
Intelligence is a process, not a fixed, gene-determined, thing. This process begins very early on, before we can even really see it, and we therefore often confuse these early, invisible stages with some sort of innate giftedness. Then we test kids and report the results as innate differences -- this one is gifted, this one is not. This one has extra promise; that one does not. We send the "gifted" ones to good schools with small class sizes, better-trained teachers, better infrastructure, better relationships with parents, and higher expectations. We send the apparently-unpromising kids to under-funded, teach-to-test schools with minimal expectations.
And then we tell ourselves that we live in an educational meritocracy. Jennifer Senior's piece helps expose that fallacy.