It's the only makeup I wear, because I have acne, but usualy by 8th hour it's gone and I look like crap. I cannot retouch my makeup because we are not allowed to go to the bathroom between classes or during class, and during lunch we have Bible study...

Use a concealer that lasts ore then 8 hours.Put on the concealer then use press powder to really seal it in! Good Luck!

Well, buying a qualify concealer is something you should definitely start with. Mineral makeup is all the rage right now, and it works pretty well, too, so looks into Bare Escentuals or Everyday Minerals if you haven't already. It lasts fairly long and it's good for your skin too! Everyday Minerals gives out free samples that are pretty generous in size by the way, so you might want to take advantage of that. Everyday Minerals is also super cheap and economical.

www.everydayminerals.com
www.bareescentuals.com

But, if you're trying to cover more serious acne, I'd suggest liquid, cream or stick concealers from Shiseido and Chanel. Of course, getting treatment rather than trying to cover up is most and foremost important, but I'm sure you know all that already. Also, I'm suggesting these big names, because the makeup found in drugstores usually perform less effectively. That's why they're cheaper, duh.

Wearing waterproof concealer also helps. Think of it as waterproof mascara. Use waterproof concealer and you probably won't have to worry about it for the entire day (the waterproof stick concealer from Shiseido works very well, this I know from personal experience). Experiment with different brands, but generally stay away from drugstore makeup.

But remember, after eight hours, your makeup will fade no matter how well it's done or what products you use. The better products you use and the better you apply your makeup, the chances are, your makeup won't fade to a point where it's visible, but it will fade just a teeny bit. So I lastly suggest carrying a mirror!!!

Sorry, it won't last all day
and why are you not able to go to the bathroom!?
what if you have to pee!?
Hmm.. The only thing I can think of is trying to retouch it when you get a chance.. or in class, sneakily or something
But I wouldn't worry, you probably look just fine without it, if it's only acne you are trying to hide you can get rid of it!. I heard Pro-active works really well.. or go to visit a dermatologist

Try this one from Revlon, it has acne medicaiton in it, so it heals as well as hides: http://www.revlon.com/ProductCatalog/ProductDetails.aspx?CategoryID=1&SubCategoryID=2&P roductID=7 Don't use it under your eyes though! Top with some powder and you'll be looking good all day.