And for the high school student who's about to ask "What's Phi Beta Kappa?" AOA is like Phi Beta Kappa which is a lot like high school honor societies such as "Arista," "Beta Club," or "Key Club."
As for AOA in med schools, I should modify my original statement. Not all 125 medical schools have a chapter of AOA. AOA policies at schools in terms of selection are different. AOA policies in terms of announcing who's who and who's not are equally different.
1. SOME schools will not announce which of their students are AOA until AFTER the all-important Dean's Letter is released.
2. SOME schools will not even announce who is AOA until AFTER the Match.
3. Then, of course, there are OTHERS who will announce AOA TWICE -- once in the middle of third year and then again right before the application/interview season for residency starts -- for some rather obvious benefit to the ultra-elite and just the regular elite, respectively.
In terms of AOA's importance on residency applications, for most of the competitive specialties and the choosy programs in the relatively non-competitive specialties, it's quite important. Heck, there's even a section on the Electronic Residency Application Service (ERAS) form that asks about a student's AOA status.
A final note: Alpha Omega Alpha is only found in US Allopathic Med Schools. The Osteopathic Schools have their own version of AOA. I don't know how important the DO equivalent of AOA is in terms of application. Being an MD student who's a member of the American Osteopathic Association (also reduced to "AOA") does not warrant the checking of the AOA box on the ERAS form.