Sorry I think I misunderstood you, I thought you meant you scheduled an interview at school A first, then school B decided to offer you an interview on the same day as.school A...and you wanted to ask school A to reschedule so you could attend school B'a interview...
But anyways, the way you explained it sounds fine, I just wouldn't say anything about another school. Make something else up, maybe.
Sorry I misunderstood you the first time