If you do get another chance to make a presentation to the principal you should make sure he knows what your outfit will entail, i.e. what you will look like when you show up for the event. If you have everything you need you could get dressed up and have your parents take a series of photos of you from various directions to show the principal. Better yet, if you get an appointment with him to discuss it ask if it is okay for you to wear your outfit to the appointment so he can have first hand opportunity to see just exactly what you are talking about. Take photos of folks from this forum dressed similarly to show that your outfit is indeed standard and traditional highland wear of appropriate scottish heritage attire, and not just some kid in a "joke" or "costume" kilt. A good place to poach some pictures would be the thread by Panache and McMurdo about the 10 different levels of dress with a kilt.

Again, good luck, and keep us posted. Let us know if there is ANYTHING we can do to help.

jeff