I don't know how it is in the US, but in Australia, schools have all the emergency details on file, and that information is given out on an as needed basis. If you are doing a school show, then you will (no doubt) have a member of the faculty involved in some respect, and there is a good chance they will be required to attend all off-campus rehearsals/shows/etc. Talk to that person; there is a good chance that the teacher will know correct proceedure when faced with an emergency involving a pupil on an excursion.
Tread carefully. Your level of responsibility (as far as actors health) is a lot different in the school world than the professional world. Combined with the sensitive nature of medical information, you may face a lot of opposition in your desire to be professional.