Question: Does single-choice Early Action, which is offered by schools like Harvard and Yale, mean that I cannot apply to other colleges during both the Early Action AND regular decision periods? How do colleges know that single-choice EA or Early Decision candidates haven't applied elsewhere?
Harvard, Yale and other colleges that have "single choice early action" programs do not allow candidates to apply to other schools during the early-action period only. However, once they receive EA (Early Action) decisions (mid-December), then applicants are free to apply elsewhere, if they so choose.
Some colleges with early options exchange lists of admitted students, once their picks have been made. Therefore, if you apply early to such a college and you are admitted, then other colleges will see your name on that list. If you are not admitted, then the other schools will never know you applied elsewhere. But even when colleges don't check up on early applicants, your signature--and your honor--is still on the line.
According to Patricia Wei, associate director of undergraduate admissions at Yale, "When students sign the EA form, they are indicating that they are not applying to any other schools' early programs. We expect our applicants to be ethical and abide by this contract. Yale does not share EA lists with other colleges, but should the Yale Admissions Office find out that a Yale EA candidate has also applied to other Early Action or Early Decision programs, we may rescind our offer of admission and we may contact the other colleges to which the student has applied EA or ED. It will be up to the other colleges what actions they will take."
Thus, if you are applying to college via a single-choice early option, and you attempt to also apply elsewhere before it's permissible, then your integrity is certainly at stake and possibly a lot more.