I'm in nursing school too. I was summoned last month, and I just sent them a letter stating that I was in school and could not attend. I made sure I included the name of the school and the school's phone number in case they needed to verify anything with the school. A week later I got a phone call that said I was excused from jury duty.
It can't hurt to send them a letter and see what happens! I know with my school, we can't miss more than 10% of class each semester or we are dropped from the program. If we do miss even one day we have to make it up by coming to school on semester break, or if we miss clinicals they have to schedule a clinical day with a hospital for us to make it up on our break. I am not willing to miss any days unless it's absolutely necessary!