If you live in an area with a higher number of highly educated parents this doesn't shock me at all. Especially if they are using 90th%ile in which case statistically it should be ~10%. 17 is higher than 12 but not crazy.
My kids started in a school of ~500 kids (spread out over 8 grades). They don't screen until 5 year in but some families end up testing privately before then because their kids are going off the rails (we started this adventure because school was a disaster and they were convinced DS was ADHD and told us to test). I know 5 kids that all transferred out of this school (3 are in the same grade) into a program in another board with a 99.6% WISC GAI or FSIQ cut off. We didn't meet until we had all moved out of the school. They all ended up testing under similar scenarios to ours and in these cases, no one was testing in the hopes of accessing gifted programming since we all didn't know there was anything like that until after testing. There are books in their houses and attentive parents but we are not talking hot housing in these cases.
Statistically, that is way higher than the ~2 kids expected but we live in a place where masters and PhD's are common. People moved here from all over the country/world for work, met highly educated partners, gravitated towards good neighbourhoods and had children. It turns out the bell curve is a little skewed in some areas.
