I attend a very prestigious high school which does not rank; only a school profile showing the lowest and highest GPA is submitted to colleges. However, I’ve been informed that I have the highest GPA, so I would’ve been rank #1 (of ~500). I’d assume this would be a big boost for my application given the rigor of my school. Is this something worth mentioning in my application (such as in “Additional Info” section) or is this commonly checked anyway by the admissions office, and will look bad if I include it myself?
No.
That is the kind of information that either your GC will include in their recommendation letter,
or
when applying to highly selective colleges from a “very prestigious high school” there should be enough applicants from your HS that admissions officers will have a very, very good idea how your GPA compares to others at you hs.
Don’t do it. If your school report says that the school doesn’t rank, but then you report yourself as number 1, it will look like you are making it up.
Then you would be wrong in your assumption.
Don’t list something that will not match what the GC lists. If the school does not rank, then it (like over half the schools in the US) does not rank. AOs all went to college; they can extimate your rank from the school profile if they are no inclined. But the difference between a rank of 1 vs rank of 5 in a class of 500 is inconsequential.
You can ask your GC to include that info in the school REC
Based on this why would you even have to mention being #1? Your GPA will be listed as the highest. I think the college will figure it out.