While schools may or may not have a master list of excepted/deposited students, that doesn’t mean that the head of admissions doesn’t know the head of admissions from multiple other schools. Also some applications have a section for you to fill in the other schools that you applied to. It comes down to a matter of ethics. Is this the lesson that you want to teach your child? Are you willing to except that your child might get rescinded at both school and end up with no college? One thing that you might try is to get an exact date of notification from school B and once you have that, ask school A for an acceptance extension. This way you are not double dipping.