14% of students at 90th percentile or above wouldn't be unusual in the area I'm in. Since an ability test was used for screening, I doubt you're looking at hot-housing but rather the general makeup of families that are sending students to this particular school.
The one thing that I don't see mentioned above (I just glanced quickly) is the school's response to parents who's kids don't make the program cut-off (wherever it falls). In our district, it's sometimes possible to advocate your child into the program not through scores, but through semi-close scores and a parent who's extremely determined to get the child into the program. I think you'd see more of this in early elementary... it's just my experience but when my kids were in K-1 it seemed like every other parent we were around thought their child was gifted.... and that's one thing that definitely dropped off by third grade (the parent-thinking-child-was-way-gifted factor).
Best wishes,
polarbear
