In the latest version of PowerPoint 2011 for Mac and PowerPoint 2013 for Windows, the default view when giving a presentation is the Presenter View. This will cause the i>clicker toolbar and results graph to show up on your screen instead of the projection screen your students see. To correct this, there are two options
The i>clicker toolbar can be moved around the screen by clicking and holding on the dark grey, left-most area of the toolbar. If you move the toolbar towards the edge it will "jump" from your presenter screen and appear on the projected display your students are viewing. Depending on the configuration of the classroom, this could mean moving ("dragging") the toolbar off to the left or to the right of the screen. This is a feature of your operating system, and is the same no matter which application you're using (Keynote, PowerPoint, or otherwise).
2. If you don't want to use Presenter View, you can turn it off.
Click on the Slide Show tab
Windows: Un-check Use Presenter View | Mac: Click Mirror Show