Occasionally I'll get contacted by someone at any of my past alma maters asking for donations. And I have no interest whatsoever donating to schools that already have huge endowments and contribute to the cataclysmic student debt problem in America by extorting untenable tuitions and fees out of kids who don't know any better, meanwhile academia has completely gone off the deep end. I am not giving you any of my money when your shady practices and impractical education is keeping me poor as is.
Edit: high schools are another matter. I briefly worked at a couple struggling private schools, and in those cases it can make a difference, but like anything else, you're not obligated to give anyone money for anything. Like a small Catholic school with a strong mission I might support, especially if I have connections there (like in the future if I want to send kids there). But if you had a bad time as a student there, why would you give them your hard earned money?