If you are presenting your portfolio in person, generally schools want to see the real art works.
If you have done a huge work of art, bringing visual documentation makes it possible for others to view it.
However, if your doing an interview in person, I'd bring something that is a photo,digital print etc of your work rather than a slide if you need one,.
Slides are hard to make out, when you have to hold them up to the light etc, just to see the image.
Make it easy and pleasurable for the person viewing your art to see it.
A nice, in focus photo print of your monumental sculpture or painting would do it!
The size of your work is unimportant, compared to its quality.
Only bring your best work to the interview no matter what size it is.
Sketchbook size is unimportant.
We just had one of our students apply to OCAD here in Toronto.
If I can get a few samples from his portfolio, I'll post them here to help you get an idea of what works.
Gerard Sternik / Director
Animation Portfolio Workshop