That 90th percentile doesn't guarantee a slot in a G&T program. It's kind of an elaborate system, but depending on what district your child is in or what school you're considering, the effective cutoff can be much higher. For example, my son's program only admitted children with either a 98 or 99 when he got into it 4 years ago. In a district like ours (District 3, which is basically the Upper West Side), a score of 90 won't get you a spot anywhere, unless...
...you have a child with a 90 with a sibling already in a program. If one child tests into a program, then later siblings are given preference over children without a sibling in the school, as long as they have a score over 90.