As far as portfolios go, you're generally right, but like I said every school is different. Since I don't think design is really part of any high school curriculum, usually those portfolios are looking more for core artistic skills. You can probably wow them with design work in there, but I'm sure they'll also want to see things like figure drawings, still life, scuplture, etc.
I don't think you need to do anything a year early, you might be thinking of early admission/early decision, which is what some students do to try and secure their place at their top choice school. Basically that says "I'm applying extra early cause I want to go here, and if I get accepted I'm definately going". Ensures them that if they offer you a spot, they get your money. That also varies between schools though. If you have certain schools you're interested in then check out their websites, they'll have the whole admissions process. I don't think you have to start worrying until the end of 11th grade though.
I didn't get into the ID program I applied to that required a portfolio...of course that might have been due to the fact that my teacher didn't know how to work her camera, so all of the slides we had to send (before the glory days of the PDF file) were out of focus, or in focus but taken with a $10 disposable camera. I suppose in hind sight maybe that worked out for the best though. Syracuse was too cold for my tastes anyways.