Does being Hispanic and fluent in 3 languages help much at all for the typical selective prep school?
You are a smart kid . You really need to ask this question?
I know it helps. My question is how much?
Being Hispanic is the key. Fluent in multiple languages is gravy. Of course what else have you got to offer? Here are many talented minority applicants.
Based on posting history, the OP is a parent.
In the grand scheme of things, not much. It’s not that uncommon, especially when the international applicants come into play. Hispanic, depending on the school, will count for much more.