sure, you're qualified! Granted, you may need a bit of a refresher for the things that you haven't done on a regular basis, but it doesn't make you less of a nurse.
In fact i applied for a staff nurse position at a local hospital about a year ago and was instead given a per diem job as an adn. ok.. still not totally flexing all of my bedside skills, but let me tell you, it's like riding a bike - i have to respond to all codes and trust me - it all comes rushing back!
It sounds like you enjoy your school nurse job. Don't let that go! Job satisfaction is a valuable thing in and of itself!
If you are feeling the need for a little clinical challenge, maybe you should consider picking up a little per diem work to keep your skills sharp or maybe volunteer with a first aid squad near by - sure ems and nursing are different things, but where they do over lap may fill that void.