Now, Jennifer Senior has a long article in New York, The Junior Meritocracy, questioning the wisdom of handing out lifetime prizes at age four. Surely, she asks, wouldn't it be better to, say, test at age seven, when IQ testing is more accurate?
I'm familiar with a public high school program only open to kids with stratospheric IQs of 145 or higher. Within the school there tend to be two groups of kids: those who scored >=145 on an IQ test in 8th grade, who are really smart; and those who got into this program's feeder programs in third grade. The kids who are in this high school because they scored >=145+ in second grade tend to be smart, but often not outlandishly smart, simply because of the lower accuracy in testing at earlier ages and a tendency toward regression toward the mean over time. Testing 4-year-olds just exacerbates all this.
My guess is that testing at age 4, despite its high degree of arbitrariness, is popular with New York City parents because it lets them decide whether they will stay in Manhattan / Brooklyn or move to a suburb where the open enrollment schools have good students on average. If your kid gets into an exclusive public program or into a famous private school, then we'll stay in the city. Otherwise, Fort Lee, here we come!
The summer before he starts school is a pretty easy time to move a kid. After that, he'll have school friends, and he'll be old enough to complain more.