How hard is Physician's Assistant school?
It's harder to get into PA school than it was for me to do well in PA school. It is hard, but it needs to be hard because lives are in our hands. If you want it bad enough you will do well, if you expect to have a lively social life during school you might not make it.
If you are in nursing school I recommend becoming a nurse and then going on to be a nurse practitioner! NP and PA essentially do the same thing!
I see your question was posted a while ago. Have you decided which path to take? I'm a current PA student, so let me know if you have any specific questions. Also, feel free to look at the information here on becoming a PA: