I wasn't in adult care, but wanted to encourage you to review the primary pediatric ailments you see in a school clinic, such as asthma, adhd/add. About 80% of pediatric codes are due to respiratory failure, not cardiac issues. Honestly, 6th-8th is a great age and a lot of what you see in a school clinic is basic first aid/emergency response, meds, asthma, colds, "someone accidently stabbed me with a pencil," social/emotional issues and more. Clinically speaking, the cases you typically see are not that challenging and any good nurse should be able to handle them with a little pedi review. What some of the biggest differences may be is dealing with parents, administrative work, screenings, being the only medical professional in the building, and just learning the ropes of the educational system vs a healthcare system. They are very different. I'd stress your experience working with families, patient education, and heart for community health, along with any experience you may have with children outside of nursing. Good luck!
ETA: You also will be triaging the adult staff as well, so your adult experience will come in handy as well!