Probably not - school uniforms don't sit well with a lot of folks, and you'd certainly never get skirts of that length approved by the PTA. 
Oh yeah I forgot American doesn't wear uniformschool uniforms don't sit well with a lot of folks
I would recommend very, very strongly against doing this. Even when I was in middle/high school in the '90's, a non-student would have attracted attention - it's not like the staff don't know the students. Since Columbine and 9/11, many (most?) schools would have you arrested and charged for that. Depending on where you are, there may be security at the entrance, but staff will catch on quickly if not.If I were to walk into the school saying I'm students no one would notice would it?