Some of the boarding school solicitations sent to my son last year stated that for scholarship consideration, ISEE scores at or above 90% are expected. However, what score is considered good will vary by school. And remember, these are not general population percentiles. Just a guess, but I would think that any student who applies to a school requiring the ISEE falls MINIMALLY in the top half on a regular nationally normed grade level test such as ITBS.
To correct for my post last year; My daughter did not take the SSAT, but rather the fairly common Catholic/private high school entrance exam (don�t remember the acronym).